AN  INTRODUCTION        :,; 

TO  THE 

ANALYTICAL  CHEMISTRY 

OF  THE 

RARER  ELEMENTS 


BY 

LOUIS  J.   CURTMAN 

Assistant  Professor  of  Chemistry,  Chief  of  the  Division  of 
Qualitative  Analysis,  College  of  the  City  of  New  York 


NEW    YORK 


LJ 


COPYRIGHT,  1922, 

BT 

LOUIS   J.    CURTMAN 


PRESS  OF 

BRAUNXVORTH   &  CO. 

BOOK  MANUFACTURERS 

BROOKLYN,   N.  Y. 


PREFACE 


THE  experiments  described  in  this  book  are  designed  to  lay  a 
sound  foundation  for  the  analytical  study  of  the  rarer  elements. 
The  great  economic  importance  attained  by  these  metals  in  the 
last  decade  indicates  the  imperative  need  of  introducing  into  our 
colleges  and  universities  a  course  of  instruction  such  as  is  given  in 
this  book.  Lectures  and  text-book  study  unsupported  by  adequate 
laboratory  practice  are  ineffective  in  this  essentially  experimental 
field.  The  author  wishing  to  give  his  students  a  brief  laboratory 
course  in  the  rarer  elements  in  which  the  analytical  side  would  be 
emphasized,  looked  about  in  vain  for  a  suitable  text.  He  there- 
fore prepared  this  series  of  experiments  to  meet  his  requirements. 
Every  experiment  described  in  this  manual  was  personally 
performed  and  repeated  by  the  author.  As  is  well  known,  the 
results  obtained  in  preliminary  experiments  in  qualitative  analysis 
depend  not  only  upon  the  concentrations  of  the  test-solutions  used, 
but  also  upon  the  strengths  of  the  reagents  employed.  To  this 
end,  test-solutions  of  known  concentrations  are  invariably  em- 
ployed. The  preparation  of  these  solutions  is  facilitated  by  the  use 
of  the  author's  special  table  giving  the  quantities  of  the  salts  or 
compounds  to  be  used  in  each  set  of  experiments.  To  insure 
further  definiteness  in  the  results,  directions  are  given  for  pre- 
paring the  reagents  to  be  used  in  making  the  tests. 

A  laboratory  course  in  the  rarer  elements  is  often  objected 
to  on  the  ground  that  the  materials  required  are  expensive.  To 
meet  this  difficulty,  it  was  necessary  first,  to  provide  that  in  each 
test  a  very  small  though  definite  quantity  of  metal  be  used; 
second,  to  carry  out  numerous  experiments  to  determine  the  con- 
ditions under  which  conclusively  visible  results  could  be  obtained 
when  using  small  amounts  of  metal.  Both  of  these  tasks  have  been 
successfully  accomplished.  From  the  total  quantity  of  material 
used  in  any  series  of  experiments,  it  will  be  apparent  that  even  with 

3 


500154 


4  PREFACE 

large  classes,  the  cost  of  the  material  will  not  be  considerable. 
To  further  reduce  the  cost,  provision  should  be  made  to  recover 
the  more  expensive  metals  from  the  students'  waste  solutions. 

This  book  may  be  used  to  complete  a  one-year  course  in  Quali- 
tative Analysis.  Or  it  may  serve  as  an  introductory  text  in  a 
special  course  on  the  rarer  elements  in  which  lectures  are  given, 
analyses  made,  and  in  which  provision  is  made  for  consulting  the 
fairly  rich  literature  of  this  subject. 

The  author  will  be  grateful  for  constructive  criticism  or  sug- 
gested improvements. 

L.  J.  C. 

NEW  YORK  CITY, 
Oct.,  1921. 


TABLE  OF  CONTENTS 


PAGE 

PREFACE 3 

REFERENCE  BOOKS  ON  THE  RARER  ELEMENTS 7 

TABLE  OF  ATOMIC  WEIGHTS 8 

DIRECTIONS  FOR  THE  PREPARATION  OF  REAGENTS 9 

TABLE  FOR  THE  PREPARATION  OF  TEST-SOLUTIONS 12 

THE  ANALYTICAL  CLASSIFICATION  OF  THE  RARER  ELEMENTS 13 

EXPERIMENTS  ON  THE  RARER  ELEMENTS 16 

GROUP  1.  Thallium. '. 16 

Tungsten 17 

GROUP  2.  Ruthenium 19 

Rhodium 20 

Palladium 21 

Osmium 23 

Platinum 24 

Iridium 27 

Gold 28 

Selenium 31 

Tellurium 33 

Molybdenum 34 

GROUP  3.  Beryllium 36 

Titanium 38 

Thorium 40 

Zirconium 41 

Columbium 44 

Tantalum 46 

Uranium 47 

Cerium 50 

Lanthanum 53 

Praseodymium 54 

Neodymium 55 

Yttrium 56 

5 


6  CONTENTS 


PAGE 

Erbium 58 

Vanadium 59 

GROUP  5.  Lithium 61 

Rubidium 62 

Caesium.  .  63 


REFERENCE  BOOKS  ON  THE  RARER  ELEMENTS 

CROOKES.     Select  Methods  in  Chemical  Analysis. 

CLASSEN.    Ausgewahlte    Methoden    der    analytischen    Chemie. 

Erster  Band. 
FRESENIUS.    Qualitative  Chemical    Analysis.     Translated    by 

Mitchell,  1921. 
SCHOELLER  AND  POWELL.     The  Analysis  of  Minerals  and  Ores  of 

the  Rarer  Elements. 

BROWNING.     Introduction  to  the  Rarer  Elements. 
A.  A.  NOTES.     Technology  Quarterly,  16,  93-131,  17,  214-257. 
A.  A.  NOTES  AND  BRAT.    Journal  Amer.  Chem.  Society,  29  (1907), 

137-205. 
A.  A.  NOTES,  BRAT  AND  SPEAR.    Journal  Amer.  Chem.  Society, 

30  (1908),  481-563. 

NEWTON-FRIEND.     Text-book  of  Inorganic  Chemistry.     10  vols. 
ROSCOE  AND  SCHORLEMMER.    Treatise  on  Chemistry.     (Vols.  1 

and  2.) 

ABEGG.     Handbuch  der  anorganischen  Chemie. 
SPENCER.     The  Metals  of  the  Rare  Earths. 
R.  J.  METER  AND  0.  HAUSER.    Die  Analyse  der  seltenen   Erden 

und  der  Erdsauren. 

BOHM.    Die  Darstellung  der  seltenen  Erden.     (2  vols.) 
TRUCHOT.     Les  Terres  Rares. 
HERZFELD  AND  KORN.     Chemie  der  seltenen  Erden. 


ATOMIC  WEIGHTS,  Corrected  to  1920 


cci  ,  .^.  *,«.<  ^fcm^  ^  Cc-c  i.c< 

bym- 

Atomic 

Name 

Sym- 

Atomic 

bol. 

Weight. 

bol. 

Weight. 

Aluminum  

Al 

27  1 

Molybdenum 

Mo 

96  0 

Antimony  (Stibium) 

Sb 

120.2 

Neodymium  

Nd 

144.3 

Argon 

A 

39  9 

Neon 

Ne 

20  2 

Arsenic  

As 

74  96 

Nickel      .              .... 

Ni 

58  68 

Barium  

Ba 

137  37 

Niton 

Nt 

222  4 

Bismuth 

Bi 

208  0 

Nitrogen 

N 

14  01 

Boron 

B 

10  9 

Osmium 

Os 

190  9 

Bromine  

Br 

79  92 

Oxvjren 

o 

16  00 

Cadmium  . 

Cd 

112  40 

Palladium 

Pd 

106  7 

Caesium  

Cs 

132  81 

Phosphorus  

P 

31.04 

Calcium  

Ca 

40  07 

Platinum 

Pt 

195.2 

Carbon  . 

c 

12  005 

Potassium  (Kalium) 

K 

39.10 

Cerium  

Ce 

140  25 

Praseodymium  

Pr 

140.9 

Chlorine  

Cl 

35  46 

Radium               .    ... 

Ra 

226.0 

Chromium 

Cr 

52  0 

Rhodium 

Rh 

102  9 

Cobalt  

Co 

58  97 

Rubidium    

Rb 

85.45 

Columbium  (Niobium) 
Copper  (Cuprum) 

Cb 

Cu 

93.1 
63  57 

Ruthenium  
Samarium 

Ru 

Sa 

101.7 
150  4 

Dysprosium  

Dy 

162  5 

Scandium  

Sc 

44.1 

Erbium  . 

Er 

167  7 

Selenium 

Se 

79.2 

Europium 

Eu 

152  0 

Silicon 

Si 

28  3 

Fluorine  

F 

19  0 

Silver  (Argentum)  .  .  . 

Ag 

107.88 

Gadolinium 

Gd 

157  3 

Sodium  (Natrium)   .  . 

Na 

23.00 

Gallium  ^ 

Ga 

70  1 

Strontium 

Sr 

87.63 

Germanium  

Ge 

72  5 

Sulphur  

s 

32.06 

Glucinum  (Beryllium) 

Gl 

9  1 

Tantalum   .          .... 

Ta 

181.5 

Gold  (Aurum) 

Au 

197  2 

Tellurium 

Te 

127.5 

Helium  

He 

4  00 

Terbium  

Tb 

159.2 

Holmium 

Ho 

163  5 

Thallium             

Tl 

204.0 

Hydrogen 

H 

1  008 

Thorium 

Th 

232.15 

Indium  .  . 

In 

114  8 

Thulium  

Tm 

168.5 

Iodine 

I 

126  92 

Tin  (Stannum)  

Sn 

118.7 

Iridium  

Ir 

193  1 

Titanium  

Ti 

48.1 

Iron  (Ferrum)  
Krypton 

Fe 
Kr 

55.84 
82  92 

Tungsten    (Wolfram- 
ium) 

W 

184.0 

Lanthanum 

La 

139  0 

Uranium 

u 

238.2 

Lead  (Plumbum) 

Pb 

207  20 

Vanadium 

V 

51.0 

Lithium 

Li 

6  94 

Xenon  

Xe 

130.2 

Lutecium  

Lu 

175.0 

Ytterbium  (Neoytter- 

IM  agnesium 

Me 

24  32 

bium) 

Yb 

173.5 

Manganese 

Mn 

54  93 

Yttrium  

Y 

89.33 

M!  e  r  c  u  r  y  (Hydrar- 

Zinc          

Zn 

65.37 

gyrum)  

Hg 

200.6 

Zirconium  

Zr 

90.6 

AN  INTRODUCTION  TO  THE  ANALYTICAL 
CHEMISTRY  OF  THE  RARER  ELEMENTS 


PREPARATION  OF  REAGENTS 

CONCENTRATED  ACIDS 

Cone.  HC1.  12N.  Sp.  gr.  1.19  contains  about  38  per  cent 
HC1  by  weight. 

Cone.  HNO3.  16N.  Sp.  gr.  1.42  contains  about  70  per  cent 
HNO3  by  weight. 

Cone.  H2SO4.  36N.  Sp.  gr.  1.84  contains  about  96  per  cent 
H2S04  by  weight. 

Cone.  HF,  contains  about  48  per  cent  HF. 

H2SO3.  A  saturated  aqueous  solution  of  S02  at  15°  contains 
about  16.5  per  cent 


DILUTE  ACIDS 

Dilute  HC1.  3N.  Mix  25  cc.  cone.  HC1  with  sufficient  water 
to  make  the  volume  100  cc. 

Dilute  HNO3.  3N.  Mix  19  cc.  cone.  HN03  with  sufficient 
water  to  make  the  volume  100  cc. 

Dilute  H2SO4.  3N.  In  a  beaker  containing  80  cc.  of  distilled 
water,  add  with  constant  stirring  8.3  cc.  of  cone.  H2SO4.  Cool  the 
solution  to  room  temperature  and  then  add  sufficient  water  to 
make  volume  100  cc. 

Tartaric  Acid.     Make  a  saturated  aqueous  solution. 

Oxalic  Acid.     H2C204  •  2H2O.     2N.     126  g.  per  liter. 

BASES 

Cone.  NH4OH.  15N.  Sp.  Gr.  0.90  contains  about  28  per 
cent  NH3. 

Dilute  NH4OH.  3N.  Dilute  20  cc.  of  cone.  NH4OH  with 
80  cc.  of  water. 


10        _  .    .    .--RARER  ELEMENTS 

Sodium  Hydroxide.  6N.  Use  only  NaOH  purified  by  alcohol 
or  reagent  NaOH.  This  grade  contains  about  4  per  cent  of  water. 
Hence  the  amount  necessary  to  make  100  cc.  will  be  GXf&XV^ 
=  25  g.  Dissolve  this  quantity  of  NaOH  in  80  cc.  of  water,  cool  the 
solution  and  then  add  sufficient  water  to  make  the  volume  100  cc. 
Filter  through  cotton  if  the  solution  is  not  perfectly  clear. 

SOLUTIONS  AND  LIQUID  REAGENTS 

Alcohol  Ethyl.     C2H5OH.     95  per  cent  by  volume. 

Alcohol  Methyl.    CH3OH. 

Ammonium  Acetate.    NH4C2H302.    3N.    250  g.  per  liter. 

Ammonium  Carbonate.  (NH4)2C03.  Saturated  aqueous 
solution. 

Ammonium  Chloride.    NH4C1.     Saturated  aqueous  solution. 
Ammonium  Oxalate.     (NH4)2C204-H2O.     Saturated  aqueous 
solution. 

Ammonium  Sulphide  (colorless).  (NH^S.  Saturate  100  cc. 
of  cone.  NH4OH  with  H2S  and  add  100  cc.  of  cone.  NH4OH. 
Dilute  the  solution  with  300  cc.  of  water. 

Ammonium  Polysulphide.  (NH4)2S*.  Digest  the  colorless 
undiluted  (NH4)2S  with  flowers  of  sulphur  in  the  proportion  of 
1  gram  to  the  liter  and  then  dilute  the  solution  with  an  equal 
volume  of  water. 

Antimony  Trichloride.  SbCl3.  Dissolve  18.8  g.  in  100  cc. 
HC1  (1  :  1). 

Barium  Chloride.    BaCl2.    2H20.    N.     122  g.  per  liter. 

Bromine  Water.    A  saturated  aqueous  solution. 

Cupferron.     6  per  cent  aqueous  solution. 

Dimethylglyoxime.  Treat  1  g.  with  100  cc.  95  per  cent  alcohol. 
Heat  to  hasten  solution. 

Formaldehyde.    HCHO.    40  per  cent  aqueous  solution. 

Hydrochlorplatinic  Acid.  H2PtCl6  •  6H20.  10  per  cent  solu- 
tion. 

Hydrogen  Dioxide.     3  per  cent  solution. 

Hydrogen  Dioxide.     30  per  cent  solution. 

Magnesia  Mixture.  Dissolve  110  g.  MgCl2-6H20  and  280  g. 
NH4C1  in  1  liter  of  distilled  water;  when  solution  is  complete,  add 
261  cc.  of  NH4OH-(Sp.  gr.  0.90),  then  add  enough  water  to  make 
the  volume  2  liters. 

Mercuric  Cyanide.    Hg(CN)2.    N.     126  g.  per  liter. 


REAGENTS  IN  SOLID  FORM  11 

Metanitrobenzoic  Acid.    0.4  g.  in  100  cc. 

Potassium  Bromide.     KBr.     0.5N.     60  g.  per  liter. 

Potassium  Chromate.    K2Cr04.    N.    97  g.  per  liter. 

Potassium  Ferrocyanide.  K4Fe(CN)6*3H2O.  N.  105  g.  per 
liter. 

Potassium  Fluoride.    KF.    3N.     174  g.  per  liter. 

Potassium  Iodide.     KI.     0.5N.    83  g.  per  liter. 

Potassium  Nitrite.     KN02.     500  g.  per  liter. 

Potassium  Sulphate.    K2S04.     Saturated  aqueous  solution. 

Potassium  Sulphide.    K2S.    0.5N.    27.6  g.  per  liter. 

Potassium  Thiocyanate.    KCNS.    N.    97  g.  per  liter. 

Sodium  Carbonate.    3N.     159  g.  per  liter. 

Sodium  Cobaltic  Nitrite.  Na3Co(N02)G.  Dissolve  100  g.  of 
NaN02  in  300  cc.  of  distilled  water.  Slightly  acidify  the  solution 
with  acetic  acid  and  then  add  10  g.  of  Co(N03)2-6H2O.  Allow 
the  solution  to  stand  for  24  hours  and  filter  if  necessary. 

Sodium  Phosphate.    Na2HP04  -  12H20.     N.     119  g.  per  liter. 

Stannic  Chloride.    SnCU  •  5H20.     29.5  g.  in  100  cc. 

Stannous  Chloride.  0.5N  in  3N-HC1.  Dissolve  5.7  g.  of 
SnCl2  •  H2O  in  25  cc.  of  cone.  HC1.  Stir  and  heat  if  necessary  till 
solution  is  complete.  Add  sufficient  water  to  make  the  volume 
100  cc.  To  prevent  the  solution  from  oxidizing  keep  the  solution 
in  a  glass-stoppered  bottle  containing  a  strip  of  pure  tin  foil. 

Turmeric  Solution.  Saturate  95  per  cent  ethyl  alcohol  with 
turmeric  powder  and  filter  the  mixture. 

REAGENTS  IN  SOLID  FORM 

Ammonium  Chloride.    NH4C1. 

Ammonium  Persulphate.     (NH4)2S2Og. 

Asbestos  Paper. 

Ferrous  Sulphate.    FeS04  •  7H20.     C.P.  fine  crystals. 

Lead  Dioxide.     PbO2  free  from  Mn. 

Litmus  Paper.    Blue  and  red,  to  be  kept  in  stoppered  tubes. 

Potassium  Chloride.    KC1.     C.P.  fine  crystals. 

Potassium  Carbonate.     K2COs.    Anhydrous  C.P. 

Sodium  Bismuthate.    NaBiOs. 

Sodium  Carbonate.     Na2COs.    Anhydrous  C.P. 

Sodium  Formate.    NaHC02. 

Sodium  Peroxide.     Na2O2.     Pure. 

Sodium  Sulphite.    Na2SOs.    Anhydrous. 


12 


RARER  ELEMENTS 


Sodium  Thiosulphate.    Na2S2O3  •  5H20. 
Thiourea.    CS(NH2)2. 
Zinc.     Zn. 

TABLE  GIVING  DATA  FOR  THE  PREPARATION  OF  TEST 
SOLUTIONS  OF  KNOWN  STRENGTH. 


Group. 

Metal. 

Compound. 

Formula 
Weight. 

Solubility 
in  100 
Parts  of 
Water. 

Per 

Cent 
Metal. 

Quant, 
to  Yield 
100  mg. 
of  Metal. 

1 

Tl 

T1NO3 

266.01 

106 

76.65 

0.130g. 

W 

Na2W04-2H2O 

330. 

41° 

55.75 

0.180 

2A 

Pd 

PdCl2 

177.7 

Sol.inHCl 

60 

0.167 

Rh 

RhCl3-4H2O 

281.34 

v.s. 

36.6 

0.274 

Ru 

K2RuCl6 

357.2 

s. 

28.5 

0.352 

Os 

OsO4 

254.9 

s. 

75 

0.133 

2B 

Pt 

H2PtCl6-6H2O 

517.87 

v.s. 

37.7 

0.265 

Ir 

IrCl4 

334.94 

s. 

57.6 

0.176 

Au 

HAuCl4-4H20 

412.11 

v.s. 

47.8 

0.210 

Se(ous) 

H2SeO3 

129.22 

v.s. 

61.5 

0.162 

Se(ic) 

K2SeO4 

221.40 

115° 

35.8 

0.280 

Te(ous) 

K2TeO3 

253.7 

s. 

50.3 

0.198 

Te(ic) 

H2TeO4-2H2O 

229.55 

s. 

55.5 

0.180 

Mo 

MoO3 

144 

66.6 

0.150 

3A 

Be 

BeSO4-4H2O 

177.22 

10014 

5.14 

1.950 

Ti 

TiO2-H2O 

80.10 

49 

0.204 

Th 

Th(N03)4-12H,0 

696.67 

v.s. 

33.40 

0.300 

Zr 

ZrOCl2-8H2O 

321.65 

v.s. 

28.2 

0.355 

Cb 

Cb2O6 

267 

70 

0.144 

Ta 

Ta2O6 

443 

82 

0.122 

U 

UO2(NO3)2-6H2O 

502.32 

200 

47.48 

0.210 

Ce 

Ce(NO3)3-6H20 

435.24 

v.s. 

32.28 

0.310 

La 

La(NO3)3-6H2O 

433  .  13 

v.s. 

32.09 

0.312 

Pr 

Pr(NO3)3-6H2O 

435 

s. 

32.35 

0.310 

Nd 

Nd(NO3)3-6H2O 

438.42 

v.s. 

32.91 

0.310 

Y 

Y(N03)3-6H20 

382.83 

v.s. 

23.2 

0.430 

Er 

Er(NO3)3-6H2O 

461.53 

s. 

36.26 

0.275 

3B 

V 

NaVO3 

122 

s. 

41.8 

0.239 

5 

Li 

LiCl 

42.40 

63° 

16.42 

0.610 

Rb 

RbCl 

120.91 

7610 

70.68 

0.142 

Cs 

CsNO3 

194.82 

9.3° 

68.17 

0.146 

THE  ANALYTICAL  CLASSIFICATION 


13 


THE    ANALYTICAL    CLASSIFICATION    OF    THE    RARER 

ELEMENTS 

In  the  following  table  the  rarer  elements  have  been  divided 
into  five  groups  in  accordance  with  their  behavior  towards  the 
usual  group  reagents  employed  in  systematic  qualitative  analysis. 


Group  1. 

Group  2. 

Group  3. 

Group  4. 

Group  5. 

Thallium 

Division  A 

Division  A 

Radium 

Lithium 

Tungsten 

Ruthenium 

Beryllium 

Rubidium 

Rhodium 

Titanium 

Caesium 

Palladium 

Thorium 

Osmium 

Zirconium 

(Thallium) 

Columbium 

Division  B 

Tantalum 

Platinum 

Uranium 

Iridium 

Indium 

Gold 

Gallium 

Selenium 

Cerium 

Tellurium 

Lanthanum 

Molybdenum 

Praseodymium 

Germanium 

Neodymium 

Samarium 

4 

Yttrium 

J 

Erbium 

A 

Scandium 

^ 

Division  B 

Vanadium 

Group  1 

The  precipitate  produced  by  HC1  consists  of  T1C1  and  H2WO3. 
Molybdic,  eolumbic  and  tantalic  acids  may  also  precipitate  in 
this  group,  but  they  dissolve  when  an  excess  of  HC1  is  added. 
T1C1  like  PbCl2  is  slightly  soluble  in  water  and  hence  some  passes 
into  Group  2. 


C*«^J 

ho 

wr 


14  RARER  ELEMENTS 

Group  2 

The  composition  of  the  sulphides  of  the  rarer  elements  which 
are  precipitated  by  H2S  from  0.3N  HC1  solution  is  shown  below. 
The  sulphides  have  been  divided  into  two  sub  groups  in  accord- 
ance with  their  behavior  towards  (NH4)2Sj;. 

Group  2.    Division  A.    Sulphides  Insoluble  in  (NH4)2SZ. 
Ru2S3,  Rh2S3,  PdS,  OsS4  (T12S). 

Group   2.    Division  B.     Sulphides   Soluble   in   (NH4)2S*, 
PtS2,  Ir2S3,  AuS,  Se+S,  TeS2,  MoS3,  GeS2. 

Gold  and  platinum  are  usually  found  in  both  divisions,  the 
amounts  depending  upon  the  relative  quantities  of  the  other 
metals  of  Division  B  which  are  present.  In  the  absence  of  other 
metals  of  2B,  PtS2  dissolves  only  slightly  in  (NH4)2Sa:.  When 
molybdenum  is  present  in  amounts  equal  to  or  greater  than  50  mg., 
a  moderate  quantity  remains  in  the  residue  after  extraction  with 
(NH4)2SX.  The  amount  which  goes  into  solution  under  these 
conditions  is  sufficient  however,  to  make  its  detection  certain  in 
2B,  while  the  undissolved  portion  does  not  interfere  with  the 
detection  of  the  2 A  metals.  While  thallium  is  not  precipitated  by 
H2S  in  acid  solution,  it  occasionally  comes  down  in  combination 
with  the  sulphide  of  arsenic  or  antimony.  On  treating  this 
precipitate  with  (NH4)2Sz,  T12S  is  left  in  the  residue;  hence  its 
inclusion  in  2 A. 

I  Tungsten  and  vanadium  are  not  directly  precipitated  by  H2S  in 
acid  solution  and  hence  strictly  do  not  belong  to  this  group.  If, 
wever,  the  original  solution  containing  these  metals  is  treated 
'with  (NH4)2S*  and  then  acidified  with  HC1,  WS3  and  V2S5  will 
be  thrown  down.  It  is  because  these  sulphides,  when  once  formed, 
are  insoluble  in  dilute  HC1,  that  some  writers  include  W  and  V  in 
Group  2.  Moreover,  if  the  original  substance  is  decomposed  by 
fusion  with  a  mixture  of  Na2C03  and  S,  the  aqueous  extract  of  the 
melt  will  contain  W  and  V  together  with  the  common  metals  of 
2B  as  thio  salts.  On  acidifying  this  solution,  WS3  and  V2Ss  will 
be  precipitated  along  with  the  sulphides  of  As,  Sb  and  Sn.  It  is 
important  to  remember  when  one  of  the  above  procedures  is  fol- 
lowed, that  NiS  and  CoS  will  also  be  found  with  the  sulphides  of 
2A.  In  systematic  analysis,  tungsten  would  be  precipitated  in 


THE  ANALYTICAL  CLASSIFICATION  15 

Group  1,  while  vanadium  would  remain  in  solution  until  the 
filtrate  from  Group  3  was  acidified  with  HC1,  when  ¥285  would 
come  down. 


The  composition  of  the  Group  3  precipitate  is  shown  below: 


Group  3A 

Be(OH2,   Ti(OH)4,   Th(OH)4,   Zr(OH)4,    H3Cb04,     H3Ta04 

Ce(OH)3,   La(OH)3    Pr(OH)3,     Nd(OH)3,     Sa(OH)3,    Y(OH)3, 
Er(OH)3,     Sc(OH)3,  (U02)S,  Ga2S3,   In2S3. 


Group  3B 

V2S5 

The  following  elements  also  belong  to  Group  3 ;  europium,  gad- 
olinium, terbium,  dysprosium,  holmium,  ytterbium,  and  lutecium. 
They  have  not  been  included,  because  of  their  extreme  rarity. 
As  stated  above,  vanadium  does  not  come  down  in  Group  3. 
When,  however,  the  filtrate  from  Group  3  is  acidified  with  HC1, 
V2Ss  is  precipitated.  For  this  reason  it  has  seemed  proper  to  place 
this  element  in  a  separate  sub-division. 


Group  4 

The  extremely  rare  and  costly  element  radium  (Ra)  belongs  to 
this  group.  If  present  it  will  be  precipitated  as  a  carbonate  along 
with  Ba,  Sr,  and  Ca. 

Group  5 

This  group  comprises  those  metals  which  are  not  precipitated 
by  any  of  the  group  reagents.  Of  the  rarer  elements  belonging 
to  this  group,  caesium  and  rubidium  show  a  striking  resemblance 
to  potassium  and  ammonium  in  their  chemical  relationships. 
Lithium  resembles  the  alkaline  earth  metals  in  forming  an  insol- 
uble phosphate  and  a  difficultly  soluble  carbonate. 


16  RARER  ELEMENTS 

GROUP  1.  THALLIUM  (Tl)  AND  TUNGSTEN  (W) 
THALLIUM 


In  the  following  experiments,  use  a  solution  of  thallous  nitrate 
of  strength  5  mg.  Tl  per  cubic  centimeter. 

1.  Action  of  HC1  and  Properties  of  T1C1.     To  1  cc.  of  T1N03 
solution  contained  in  a  test-tube,  add  dil.  HC1  drop  by  drop  until 
no  further  precipitation  takes  place.     Note  the  color  and  nature 
of  the  precipitate.     Write  the  equation  for  the  reaction.     Shake 
the  mixture  to  coagulate  the  precipitate  and  allow  it  to  settle. 
Carefully  decant  the  clear  solution.     To  the  precipitate  in  the 
test-tube  add  5  cc.  of  water  and  boil.     Note  that  the  precipitate 
dissolves.     Divide  the  solution  into  two  equal  portions.     To  one 
add  a  few  drops  of  dilute  H2S(>4.     Note  that  no  precipitate  forms 
(distinction  from  Pb).     To  the  other  portion  add  a  few  drops  of 
K2Cr04    solution.     The    yellow    precipitate    is    Tl2CrO4.     How 
would  you  distinguish  Pb  from  Tl?    How  does  the  solubility  of 
T1C1  compare  with  that  of  PbCl2? 

2.  Action  of  KI.     Treat  1  cc.  of  T1N03  solution  with  2  or  3 
drops  of  KI   solution.     The  yellow  precipitate  which  forms  is 
Til. 

3.  Action  of  KBr.     Repeat  Exp.  2  using  a  dilute  solution  of  KBr 
instead  of  KI. 

4.  Action  of  H2PtCl6.     By  means  of  a  pipette  introduce  on  a 
small  watch-glass  three  drops  of  T1NO3  solution.     Add  one  drop 
of  10  per  cent  H2PtCl6.     The  precipitate  is  Tl2PtCl6. 

5.  Action  of  Na3Co(NO2)6.     Add  a  few  drops  of  Na3Co(N02)6 
solution    to    1    cc.    of    T1N03    solution.       The    precipitate    is 
Tl3Co(N02)6. 

6.  Action  of  K2CrO4.    That  thallous  salts  are  precipitated  by 
K2Cr(>4  has  been  shown  in  Exp.  1.     The  precipitate  is  insoluble 
in  dilute  HN03  and  in  dilute  H2S04. 

7.  Action  of  (NH4)2S.     In  a  test-tube  treat  1  cc.  of  T1N03 
solution  with  a  few  drops  of  (NH4)2S.     The  black  precipitate 
which  forms  is  T12S. 

8.  Action  of  H2S.     In  a  small  beaker  dilute  2  cc.  of  T1N03 
solution  with  20.5  cc.  of  water.    Add  2.5  cc.  dil.  HC1  (3N).    The 
resulting  solution  the  volume  of  which  will  be  25  cc.,  will  have  the 


TUNGSTEN  17 

proper  hydrogen  ion  concentration  for  the  precipitation  of  the 
Group  2  metals  by  H2S.  Pass  H2S  into  the  solution.  Note  that 
KbS  does  not  precipitate  Tl  under  these  conditions.  If  all  the  Tl 
is  not  precipitated  in  Group  1,  where  will  it  again  appear  in  the 
course  of  systematic  analysis?  (See  Exp.  7.)  Divide  the  solution 
which  has  been  treated  with  H2S  into  two  equal  portions.  To  one, 
in  a  test-tube,  add  1  g.  of  NaC2HsO2  and  shake  the  mixture. 
To  the  other  portion  add  dil.  NH4OH  to  alkaline  reaction.  Note 
and  explain  the  formation  of  T12S  in  each  case. 

9.  Action  of  NaOH,  KOH  or  NH4OH.     (a)  To  a  few  drops  of 
TINOa  solution  on  a  small  watch  glass,  add  a  few  drops  of  NaOH 
solution.     Note  that  no  precipitate  forms,     (b)  Repeat  experi- 
ment (a)  using  a  few  drops  of  dil.  NH4OH  instead  of  NaOH. 

10.  Oxidation  of  Thallous  to  Thallic  Salts.     Introduce  into  a 
test-tube  3  cc.  of  T1NO3  solution.      Add  2  cc.  dil.  H2SO4  and  0.5  g 
(NH4)  28203.     Boil  the  solution  for  2  or  3  minutes  and  then  cool 
it  thoroughly.     Divide  the  solution  into  3  equal  portions.     To  the 
first,  add  a  few  drops  of  dil.  HC1.      Note  that  no  precipitate  forms 
(absence  of  Tl(ous)).     Make  the  second  portion  alkaline  with  dil 
NHiOH.     The  brown  precipitate  which  forms  is  Tl(OH)s   (pres- 
ence of  Tl(ic)).     Treat  the  third  portion  with  a  few  drops  of 
SnCl2  solution.     The  white  precipitate  is  T1C1,  which  precipitates 
because  of  the  reduction  of  thallic  to  thallous  ions  by  the  SnCl2. 

Note.  Chlorides  and  chromates  do  not  precipitate  thallic 
ions. 

11.  Flame  and  Spectroscopic  Tests  for  Thallium.  Place  a  few 
drops  of  TINOa  solution  on  a  small  watch  glass.     Moisten  end  of  a 
platimim  wire  with  this  solution  and  hold  it  in  the  flame.     Observe 
the  green  color  of  the  flame.     Examine  the  green  flame  with  a 
spectroscope  and  note  the  green  line. 

TUNGSTEN 

Use  a  solution  of  Na2W04-2H20  of  strength  10  mg.  W  per 
cubic  centimeter. 

1.  (a)  Action  of  Mineral  Acids.  To  1  cc.  of  Na2W04  solution 
add  1  cc.  of  dil.  HC1  and  shake  the  mixture  for  a  few  moments. 
The  white  amorphous  precipitate  which  separates  is  hydrated 
tungstic  acid  H2W04-H2O.  Heat  the  mixture  to  boiling  and 
note  that  the  precipitate  becomes  yellow  due  to  the  formation 


18  RARER  ELEMENTS 

of  anhydrous  tungstic  acid  H2WO4.  Note.  H2W04  may  also 
be  precipitated  by  HNO3  or  H2SO4. 

(6)  Influence  of  Tartaric  Acid  on  the  Precipitation  of  H2WO4. 

In  a  test-tube  treat  2  cc.  of  Na2WO4  solution  with  2  cc.  of  a  sat- 
urated solution  of  H2C4H4Oo.  Now  add  1  cc.  of  dil.  HC1  and  heat. 
Note  that  precipitation  does  not  take  place. 

Note.  From  solutions  of  metatungstates,  mineral  acids  do 
not  precipitate  H2W04.  However,  on  prolonged  boiling  in  the 
presence  of  an  excess  of  acid,  the  soluble  metatungstic  acid  is 
changed  to  the  ortho  form,  which  then  precipitates. 

2.  Action  of  H2S.      Introduce  into  a  small  beaker  1  cc.  of 
Na2WO4  solution.     Add  21.5  cc.  of  water  and  2.5  cc.  dil.  HCL 
Mix  and  treat  with  H2S.     Note  result. 

3.  Action  of  (NH^S*  and  the  Formation  of  WSs.    To  2  cc. 
of  Na2W04  solution  contained  in  a  test-tube,  add  2  drops  of  cone. 
NH40H  and  treat  the  resulting  solution  with  H2S.     Note  that  no 
precipitate  forms  but  that  the  solution  becomes  yellow.     Now 
acidify  the  solution  with  dil.  HC1  and  observe  that  a  brown  pre- 
cipitate forms.     This  is  WSs-     Heat  the  mixture  to  coagulate  the 
precipitate,  filter  and  wash  the  precipitate  twice  with  hot  water. 
To  the  WS3  on  the  filter,  add  2  cc.  of  (NH)2S*  and  catch  the  solu- 
tion in  a  test-tube.     Observe  that  WSs  dissolves  in    (NEL^Sz. 
Acidify  the  nitrate  with  dil.  HC1  and  note  again  the  precipitation 
of  WSs.      If  all  the  tungsten  is  not  precipitated  in  Group  1,  where 
will  it  again  appear  in  the  course  of  systematic  analysis? 

4.  Action  of  SnCl2.     Introduce  into  a  test-tube  2  drops  of 
Na2W(>4  solution.     Add  1  or  2  drops  of  SnCl2  solution  and  note 
the  pale  yellow  precipitate  which  results.     Now  add  2  cc.  of  cone. 
HC1  and  shake  the  mixture.     Observe  the  formation  of  a  beau- 
tiful blue  coloration.     If  instead  of  2  drops,  0.5  cc.  of  the  tungstate 
solution  is  used,  a  blue  precipitate  instead  of  a  solution  will  be 
obtained. 

5.  Action  of  Zn  and  HC1.  To  1  cc.  of  Na2WO4  solution  add  2  cc. 
of  cone.  HC1  and  a  small  piece  of  Zn.     Observe  that  the  tungstic 
acid  which  is  first  precipitated  rapidly  becomes  blue  (due  to  the 
formation  of  W205). 


RUTHENIUM  19 


GROUP  2 


Division  A.     Ru,  Rh,  Pd,  Os. 
Division  B.     Au,  Pt,  Ir,  Se,  Te,  Mo. 


RUTHENIUM 

Use  a  solution  of  K2RuCl5  (potassium  pentachlorruthenate)  of 
strength  1  mg.  Ru  per  cubic  centimeter.  It  is  best  to  add  a  little 
dil.  HC1.  to  the  water  in  which  the  crystals  of  K2RuCl5  are  dis- 
solved. A  solution  of  RuCla  containing  some  HC1  may  also  be  used 
for  the  following  experiments. 

1.  Action  of  H2S.     Introduce  5  cc.  of  K^RuCls  solution  into  a 
small  beaker.    Add  2.5  cc.  dil.  HC1  and  dilute  the  solution  with 
water  to  25  cc.     Pass  in  H^S.     Heat  the  solution  to  boiling  and 
again  treat  with  £[28  for  several  minutes.     The  black  precipitate 
which  forms  after  some  time  is  Ru2Ss.     Filter  off  the  precipitate 
and  wash  it  with  10  cc.  of  hot  water.     Puncture  the  filter  and  wash 
contents  into  a  test-tube  with  the  aid  of  10  cc.  of  water.     Boil  the 
mixture,  allow  the  precipitate  to  settle  and  carefully  pour  off  most 
of  the  clear  solution.     Divide  the  residual  mixture  in  the  test-tube 
into  two  equal  portions.     To  one  portion  add  1  cc.  of  (NH^S* 
and  warm  the  mixture.     Note  that  solution  does  not  completely 
take  place.     To  the  other  portion  add  an  equal  volume  of  cone. 
HNO3.     Boil  and  note  that  the  precipitate  completely  dissolves. 

2.  Action  of  (NH^S.     To  1  cc.  of  ruthenium  solution  add 
1  cc.  of  dil.  NEUOH.     Pass  in  EkS  for  about  thirty    seconds. 
Heat  to  boiling  and  again  treat  with  H2S.     Shake  the  mixture. 
The  black  precipitate  is  Ru2Ss. 

3.  Action  of  NaOH.    Treat  1  cc.  of  ruthenium  solution  with 
five  drops  of  NaOH.    Boil  the  solution  and  allow  it  to  settle. 
The  black  precipitate  which  forms  is  Ru(OH)s. 

4.  Action  of  Zn.     Introduce  into  a  small  evaporating  dish  2  cc. 
of  ruthenium  solution  and  1  cc.  of  cone.  HC1.     Add  a  small  piece  of 
Zn.     Note  that  the  solution  becomes  indigo  blue  in  color  and  that 
finally  metallic  Ru  separates. 

5.  Action  of  KCNS.    To  1  cc.  of  ruthenium  solution  add  1  cc. 
of  KCNS.    Heat  and  note  the  changes  in  color  of  the  solution 
which  is  first  red,  then  purple  and  finally  violet. 


20  RARER  ELEMENTS 

6.  Glow  Test  of  Curtman  and  Rothberg.    Apply  the  glow  test 
(see  Exp.  11,  under  Platinum)  to  a  few  drops  of  ruthenium  solution. 
Note  that  the  test  is  negative  (distinction  from  all  the  other  plat- 
inum metals  except  Os). 

7.  Action   of  Na2S2Os.     Introduce   into   a   test-tube   0.2   g. 
Na2S2Os  and  1  cc.  of  dil.  NH^OH.     Shake  the  mixture  till  solution 
is  complete.    Now  add  2  drops  of  ruthenium  solution  and  heat  to 
boiling.      Note  the  reddish-purple  color.      Note.     This  test  is 
capable  of  detecting  Ru  in  the  presence  of  a  large  excess  of  Ir. 

8.  Action  of  KNOo,  etc.     To  1  cc.  of  ruthenium  solution  in  a 
small  evaporating  dish,  add  Na2COs  solution  drop  by  drop  with 
stirring  until  the  solution  is  alkaline  to  litmus.    Add  3  drops  of 
KN02  solution  and  boil  the  mixture.     Transfer  the  contents  of 
the  evaporating  dish  to  a  test-tube  and  hold  the  tube  under  running 
cold  water  from  the  tap  until  it  is  thoroughly  cool.     Now  add  2 
drops  (no  more)  of  freshly  prepared  colorless  (NH^S  (prepared 
by  passing  H^S  for  30  seconds  into  2  cc.  of  dil.  NH-iOH  contained 
in  a  test-tube) .     Note  the  red  color  which  develops  in  the  tube  and 
which  on  standing  changes  to  brown. 

^RHODIUM 

Use  a  solution  of  RhCls  containing  1  mg.  Rh  per  cubic  centi- 
meter. 

1.  Action  of  H2S  and  Properties  of  Rl^Sa.  Introduce  into  a 
small  beaker  10  cc.  of  rhodium  solution.  Add  2.5  cc.  dil.  HC1 
and  dilute  the  solution  with  water  to  25  cc.  Heat  to  boiling  and 
pass  in  H2S  for  about  30  seconds.  Observe  that  little  or  no  pre- 
cipitation takes  place.  Heat  to  boiling  and  again  pass  in  H2S 
for  about  a  half  minute.  Repeat  this  process  of  boiling  and  treat- 
ing with  H2S  till  precipitation  seems  complete.  The  dark  brown 
precipitate  is  Rh2S3.  Filter  on  a  small  filter  and  wash  the 
precipitate  with  10  cc.  of  hot  water.  Pierce  the  apex  of  the  filter 
with  a  platinum  wire  and  wash  contents  of  filter  into  a  test-tube 
with  the  aid  of  a  forceful  stream  of  water  from  a  wash  bottle  using 
about  10  cc.  Heat  the  mixture  in  the  test-tube  to  boiling  and 
allow  the  precipitate  to  settle.  Pour  off  most  of  the  water. 
Shake  the  suspended  precipitate  remaining  in  the  test-tube  and 
divide  it  into  three  equal  portions.  In  a  test-tube,  treat  the 
first  portion  with  2  cc.  cone.  HNOs  and  boil  for  one  minute. 


PALLADIUM  21 

Notice  that  the  precipitate  dissolves  with  difficulty.  To  the 
second  portion  add  1  cc.  of  (NH^S*  and  heat.  Note  that  the 
precipitate  does  not  dissolve.  Treat  the  third  portion  in  a  test- 
tube  with  3  cc.  of  dil.  aqua  regia  and  boil  for  one  minute.  Note 
that  complete  solution  takes  place. 

2.  Action  of  NaOH.     To  1  cc.  of  rhodium  solution  add  1  drop 
of  NaOH  and  2  drops  of  ethyl  alcohol.     Heat  to  boiling,  shake  and 
allow  to  settle.     The  brownish-black  precipitate  is  Rh(OH)3. 

3.  Action  of  KNO2.     In  a  test-tube  treat  2  cc.  of  rhodium  solu- 
tion with  1  cc.  of  KN02  solution.    Heat  to  boiling,  shake  the  mix- 
ture and  allow  the  tube  to  stand  for  one  minute.     The  slowly 
forming  yellow  precipitate  is  K3Rh(N02)6-     Set  the  tube  aside  for 
from  five  to  ten  minutes  and  examine  again  the  precipitate  which 
has  settled. 

4.  Action  of  Sodium  Formate.     To  1  cc.  of  rhodium  solution 
add  0.2  g.  sodium  formate.     Heat  the  solution  to  boiling.     The 
black  precipitate  is  metallic  Rh.    Note.     Zn  also  reduces  rhodium 
solutions. 

5.  Glow  Test.    Absorb  a  few  drops  of  rhodium  solution  in  a 
piece  of  thin  asbestos  paper  and  carry  out  the  test  in  the  manner 
described  in  Exp.  11  under  Pt. 


PALLADIUM 

Use  a  solution  of  PdCb  of  strength  1  mg.  Pd  per  cubic  centi- 
meter. The  solution  should  contain  about  1  cc.  of  cone.  HC1 
in  every  50  cc.  of  solution. 

1.  Action  of  H2S.  Introduce  into  a  small  beaker  10  cc.  of 
palladium  solution.  Add  2.5  cc.  dil.  HC1  and  dilute  the  solution 
with  water  to  25  cc.  Heat  to  boiling  and  pass  in  H2S.  The 
black  precipitate  in  PdS.  Heat  the  mixture  to  boiling  and  allow 
the  precipitate  to  settle.  Pour  off  the  clear  solution.  Add  25  cc. 
of  water  to  the  precipitate  in  the  beaker,  boil,  allow  to  settle 
and  pour  off  most  of  the  water.  Use  small  portions  of  the  residual 
mixture  of  water  and  PdS  to  determine  the  solubilities  of  PdS  in 
the  following:  (a)  Aqua  Regia.  In  a  test-tube  add  to  a  little  of 
the  mixture,  3  cc.  of  dilute  aqua  regia.  Boil  for  about  a  minute 
and  note  that  the  PdS  completely  dissolves.  (6)  Dilute  HNOs. 
To  a  small  portion  of  the  PdS  suspension,  add  2  cc.  dil.  HNOs  and 


22  RARER  ELEMENTS 

boil.  Observe  that  the  precipitate  does  not  dissolve,  (c) 
To  another  portion  of  the  PdS  precipitate  add  2  cc. 
and  warm  the  mixture.  Note  that  the  precipitate  does 
not  dissolve. 

2.  Action  of  KL  To  2  drops  of  palladium  solution  add  1  drop 
of  KI  solution.     The  black  precipitate   which  forms  is  Pdl2. 
Now  add  3  cc.  of  KI  solution  in  excess  and  note  that  the  precip- 
itate dissolves  yielding  a  brownish-red  solution. 

3.  Action  of  NaOH.     In  a  test-tube  heat  to  boiling  1  cc.  of  pal- 
ladium solution.     Add  from  a  medicine  dropper  just  one  drop  of 
NaOH  solution  and  shake  the  mixture.     The  brown  precipitate  is 
a  basic  salt. 

4.  Action    of    NH4OH.      To    1    cc.    of    palladium    solution 
containing  2  mg.  of  Pd,  add  1  drop  of  dil.  NH4OH  and  shake  the 
solution  about  a  dozen  times.     Now  add  another  drop  of  dil. 
NH40H  and  shake.     Continue  this  process  of  adding  NH^OH 
and  shaking  until  four  or  five  drops  of  dil.  NH^OH  have  been  added. 
The  pink  crystalline  precipitate  which  forms  is  Pd(NH3)2Cl2. 
To  the  precipitate  in  the  test-tube  add  2  cc.  cone.  NH^OH  and 
heat  the  tube  to  boiling.     Note  that  the  precipitate  dissolves  to  a 
perfectly  colorless  solution. 

5.  Action  of  Dimethylglyoxime.     To  1  cc.  of  palladium  solu- 
tion add  1  cc.  of  an  alcoholic  solution  of  dimethylglyoxime.     Shake 
the  tube  and  note  the  formation  of  a  voluminous  orange-yellow 
precipitate.     Add  2  cc.  of  cone.  NH40H,  shake  the  mixture  vig- 
orously and  note  that  the  precipitate  dissolves  (distinction  from 
Ni).     Note.     The  precipitate  is  sparingly  soluble  in  water,  in 
50  per  cent,  alcohol,  and  in  dilute  acids  (method  of  separation  of 
Pd  from  other  platinum  metals  except  Pt). 

6.  Action  of  NEUCl.     On  a  small  watch  glass  introduce  by 
means  of  a  medicine  dropper,  1  drop  of  PdCk  solution  of  strength 
10  mg.  Pd  per  cubic  centimeter.  Add  1  drop  of  a  saturated  aqueous 
solution  of  NH/iCl.     Stir  the  mixture  and  scratch  the  bottom  of  the 
watch  glass  with  the  stirrer.     Observe  that  no  precipitate  forms. 
Now  add  1  drop  of  cone.  HNOs  and  stir  again.     The  red  precip- 
itate which  forms  is  (NH^PdCle. 

7.  Action  of  Hg(CN)2.     To  1  cc.  of  palladium  solution  add  1  cc. 
of  Hg(CN)2  solution.     Shake  the  tube  for  about  thirty  seconds. 
The  yellowish-white  gelatinous  precipitate  which  forms  is  Pd(CN)2. 
Note.    On  ignition  the  precipitate  decomposes  leaving  a  residue 


OSMIUM  23 

of  spongy  Pd.    By  means  of  Hg(CN)2,  palladium  may  be  separated 
from  all  the  other  platinum  metals. 

8.  Action  of  Reducing  Agents. 

(a)  Sodium  Formate.  Treat  1  cc.  of  palladium  solution  in  a 
test-tube  with  0.2  g.  sodium  formate.  Heat  to  boiling.  The 
black  precipitate  is  Pd. 

(6)  Zn-j-HCl.  To  2  cc.  of  palladium  solution,  add  1  cc.  of 
cone.  HC1  and  a  small  piece  of  Zn.  Note  that  the  solution  becomes 
colorless.  After  the  action  has  been  allowed  to  proceed  for  two 
minutes,  shake  the  mixture  and  note  the  black  flocculent  particles 
of  metallic  Pd. 

(c)  FeSC>4.  In  a  test-tube  treat  1  cc.  of  palladium  solution 
with  0.5  g.  FeS04.  Heat.  Note  the  deposition  of  black  Pd. 

9.  Glow  Test.    Apply  the  glow  test  to  a  few  drops  of  palladium 
solution,  following  directions  given  in  Exp.  11  under  Platinum. 

OSMIUM 

Note.  Osmium  tetroxide  Os04  is  the  most  common  com- 
pound of  this  element.  When  pure  it  consists  of  transparent 
water-white  crystals.  The  product  usually  met  with  in  commerce 
is  yellow.  It  dissolves  in  water  and  imparts  to  the  solution  its 
characteristic  odor  resembling  chlorine  or  ozone.  Os04  is  readily 
volatile  and  is  given  off  when  any  osmium  compound  is  heated 
with  HNOs.  If  the  vapors  are  absorbed  in  KOH,  the  latter 
acquires  a  yellow  color  due  to  the  formation  of  potassium  osmiate 
K20s04. 

Os04  +2KOH  =  K2Os04  +H2O +0. 

Use  an  aqueous  solution  of  Os04  containing  1  mg.  Os  per  cubic 
centimeter. 

1.  Odor  of  Osmic  Acid.    Note  the  odor  of  an  aqueous  solution 
of  osmic  acid. 

2.  Action  of  EkS.     Introduce  into  a  small  beaker  10  cc.  of 
osmium  solution.    Add  2.5  cc.  of  dil.  HC1  and  dilute  the  solution 
with  water  to  25  cc.   Pass  in  H2S.     The  black  precipitate  is  OsS4. 
Allow  the  precipitate  to  settle  and  pour  off  the  clear  solution. 
Add  10  cc.  of  water  and  boil  the  mixture.     Allow  the  precipitate 
to  settle  and  pour  off  the  clear  solution.     Now  add  1  cc.  of  (NH4)2SX 
and  heat  gently.     Observe  that  the  precipitate  does  not  dissolve. 


24  RARER  ELEMENTS 

3.  Action  of  NaOH  on  a  Dilute  Solution  of  OsO4.     To  1  cc.  of 

osmium  solution  add  1  drop  of  NaOH.     Note  the  yellow  color  of 
the  resulting  solution. 

4.  Action  of  Thiourea.    Treat  1  cc.  of  osmium  solution  in  a 
test-tube  with  2  drops  of  dil.  HC1  and  one  small  crystal  of  thiourea. 
Shake  the  solution  and  note  the  red  color. 

5.  Action  of  Reducing  Agents. 

(a)  Sodium  Formate.  To  1  cc.  of  osmium  solution  add  0.2  g. 
sodium  formate.  Heat  to  boiling  and  note  the  reduction  to 
metallic  Os. 

(6)  Sulphurous  Acid.  To  2  cc.  of  osmium  solution  add  2  cc.  of 
H2SOs.  Heat  to  boiling  and  note  the  indigo-blue  color  which 
develops. 

(c)  SnCl2.     In  a  test-tube  treat  1  cc.  of  osmium  solution  with 
1  cc.  of  SnCl2.     Note  brown  coloration. 

(d)  FeSC>4.     Treat  1  cc.  of  osmium  solution  contained  in  a 
test-tube  with  0.2  g.   FeSO4.     Shake  the  mixture  vigorously. 
The  black  precipitate  is  Os02. 

(e)  Na2S2C>3.     To  1  cc.  of  osmium  solution  add  0.2  g.  Na2S2Oa. 
Shake  the  solution  vigorously.       The  black  precipitate  is  OsS2 
mixed  with  S. 

Note.  Zn  in  the  presence  of  strong  mineral  acids,  precipitates 
metallic  Os. 

6.  Glow  Test.     Apply  the  glow  test  (see  Exp.  11  under  Pt)  to  a 
few  drops  of  Os04  solution.     Note  that  the  test  is  negative  (dis- 
tinction from  all  the  other  platinum  metals  except  Ru) . 

PLATINUM        t 

Use  a  solution  of  H2PtCl6  of  strength  1  mg.  Pt  per  cubic  centi- 
meter in  all  the  experiments  in  which  the  strength  of  the  solution 
is  not  specified. 

1.  (a)  Precipitation  and  Properties  of  PtS2.  Introduce  into  a 
small  beaker  10  cc.  of  H2PtCl6  solution.  Add  2.5  cc.  dil.  HC1  and 
dilute  the  solution  with  water  to  25  cc.  Pass  in  H2S  for  several 
minutes  and  observe  that  the  solution  becomes  yellow.  Note. 
More  concentrated  solutions  become  brown  due  to  the  reduction 
of  the  H2PtCle.  Heat  the  solution  to  boiling  and  treat  it  with  a 
stream  of  H2S  for  one  minute.  Heat  again  to  boiling  and  pass  in 
H2S  for  a  few  minutes.  Filter  the  precipitate  of  PtS2  on  a  6  cm . 


PLATINUM  25 

filter  paper  and  wash  it  five  times  with  separate  5  cc.  portions  of 
boiling  water.  Test  the  last  washings  for  chlorides  with  AgNOa 
and  if  still  present,  continue  the  washing  until  a  negative  test  is 
obtained.  Note.  Thorough  washing  of  the  precipitate  is  neces- 
sary in  order  to  remove  any  adhering  HC1  which  would  vitiate 
the  next  test. 

(6)  Action  of  Hot  Dilute  HNO3  and  Aqua  Regia  on  PtS2. 
Perforate  the  apex  of  the  filter  containing  the  Pt§2  with  a  platinum 
wire  and  then  enlarge  the  hole.  With  a  stream  of  water  from  a 
wash  bottle,  wash  down  the  precipitate  through  the  apex  and 
catch  the  mixture  in  a  test-tube.  Heat  the  mixture  of  Pt&2  and 
water  to  boiling  and  allow  the  precipitate  to  settle.  Carefully  pour 
off  the  clear  solution  leaving  about  1  cc.  in  the  tube.  Transfer 
one-half  of  the  mixture  of  PtS2  and  water  to  another  test-tube  and 
to  the  latter  add  1  cc.  of  dil.  HNOs.  Boil.  Note  that  the  pre- 
cipitate does  not  dissolve.  Now  add  2  cc.  of  dil.  HC1  (forming  aqua 
regia)  and  heat  to  boiling.  Note  that  the  precipitate  dissolves. 

(c)  Action  of  (NH4)2S:r  on  PtS2.  To  the  other  test-tube  con- 
taining PtS2  add  the  small  portion  of  the  filter  paper  to  which 
PtS2  adheres.  Add  2  cc.  of  (NEL^S*,  shake  for  several  minutes 
and  heat  (do  not  boil).  Filter  on  a  7  cm.  filter  and  observe  that 
the  greater  part  of  the  PtS2  remains  undissolved.  Acidify  the 
(NH4)2Sz  filtrate  with  dil.  HC1,  heat  to  boiling  and  compare  the 
precipitate  with  that  obtained  by  acidifying  in  another  test-tube 
2  cc.  (NH^Sz  with  dil.  HC1  and  boiling  the  mixture.  Allow  both 
tubes  to  stand  for  fifteen  to  twenty  minutes  and  compare  the  pre- 
cipitates which  settle  at  the  bottoms  of  the  tubes  as  to  color. 
What  can  you  say  about  the  solubility  of  PtS2  in  (NH^S*? 

2.  Action  of  (NH4)2S.     In  a  test-tube  treat  1  cc.  of  platinum 
solution  with  1  cc.  of  dil.  NH4OH.     Pass  H2S  into  the  solution 
for  a  few  moments.     Shake  and  allow  to  stand.     Observe  the  for- 
mation of  a  brown  precipitate. 

3.  Action  of  KC1  or  NH4C1.    Boil  down  in  a  test-tube  3  cc.  of 
platinum  solution  to  about  1  cc.     Cool  thoroughly  under  running 
cold  water  from  the  tap.     Add  0.5  g.  KC1  and  shake  the  mixture 
The  yellow  precipitate  is  K2PtCl6.     Note.     NH4,  Cs,  Rb  and  Tl 
form  a  similar  salt  under  the  same  conditions. 

4.  Action  of  FeSO4.     To  1  cc.  of  platinum  solution  add  1  cc. 
dil.  HC1  and  0.5  g.  FeSO4.     Boil.     Note  that  no  precipitate  forms 
(distinction  from  Au). 


26  RARER  ELEMENTS 

5.  Action  of  H2C2O4  and  H2SO3.    Note.     Neither  of  these 
reagents  precipitates  platinum  (distinction  from  An).     The  stu- 
dent may  verify  these  negative  results  if  the  supply  of  platinum 
solution  is  plentiful. 

6.  Sodium  Formate.    To  2  cc.  of  H2PtCl6  solution  containing 
1  mg.  Pt,  add  0.1  g.  sodium  formate   and  heat  the  mixture  to 
boiling.       The   black   precipitate  is   metallic   platinum.    Note. 
When  formic  acid  is  used  no  precipitate  is  obtained  until  the  solu- 
tion is  neutralized  with  Na2CO3. 


7.  Action  of  SnCl2.     To  2  cc.  of  H2PtCl6  containing  1  mg.  Pt, 
add  2  cc.  of  dil.  HC1  and  2  drops  of  SnCl2  solution.     Shake  the  mix- 
ture and  note  the  deep  orange  color  which  develops  due  to  forma- 
tion of  hydrochlorplatinous  acid. 

H2PtCl6+SnCl2  =  H2PtCl4+SnCl4. 

8.  Action  of  Zn+HCl.     To  5  cc.  of  platinum  solution  add  3  cc. 
of  cone.  HC1  and  0.5  g.  granulated  Zn.     Allow  the  action  to  con- 
tinue for  a  minute  and  note  the  black  particles  of  metallic  platinum 
which  separate  and  which  remain  after  all  the  Zn  is  dissolved. 

H2PtCl6+3Zn  =  Pt+3ZnCl2+2H. 

Note.     The  same  result  can  be  brought  about  by  using  Cd, 
Mg,  or  Al  instead  of  Zn. 

9.  Action  of  Kl.     In  a  test-tube  treat  1  cc.  of  platinum  solution 
containing  0.5  mg.  Pt  with  1  drop  of  KI  solution.     The  dark-red 
coloration  is  due  to  the  liberated  iodine  and  the  simultaneous 
reduction  of  hydrochlorplatinic  acid. 

H2PtCl6-f  2KI  =  2KCl+H2PtCl4+2I. 

Note.  This  is  an  exceedingly  delicate  test  for  Pt;  but  it  is  not 
quite  as  sensitive  as  the  glow  test  of  Curtman  and  Rothberg. 

10.  Action  of  Formaldehyde.    Note.  A  40  per  cent   aqueous 
solution  of   formaldehyde   reduces    alkaline   platinum    solutions 
giving  a  precipitate  of  finely  divided  platinum. 


IRIDIUM  27 

11.  The  Glow  Test  of  Curtman  and  Rothberg.  Pour  on  a 
small  watch  glass  0.5  cc.  of  H2PtClo  containing  0.5  mg.  Pt  per 
cubic  centimeter.  By  means  of  a  small  piece  of  thin  asbestos  paper 
held  by  a  pair  of  forceps,  absorb  a  little  of  this  solution  and  hold  it 
in  the  flame  until  all  the  water  has  evaporated.  Repeat  this 
process  of  dipping  and  heating  until  the  entire  0.5  cc.  has  been 
absorbed.  Now  heat  the  asbestos  to  redness.  Turn  off  the  gas 
and  as  soon  as  the  flame  is  out,  quickly  turn  on  the  gas  and  hold 
the  asbestos,  which  should  still  be  warm,  in  the  path  of  the  un- 
lighted  mixture  of  gas  and  air.  Observe  that  the  asbestos  glows. 
If  the  glow  is  allowed  to  die  out,  it  can  be  brought  back  again  by 
heating  the  paper  again  and  holding  it  in  the  stream  of  mixed  gas 
and  air.  Note.  By  means  of  this  test  0.002  mg.  Pt  can  be  detected. 
It  serves  also  to  detect  Pd,  Ir,  and  Rh.  For  further  details  concern- 
ing this  test/see  Jour.  Amer.  Chem.  Soc.  Vol.  33.  (1911)  pp.  718-724. 

IRIDIUM  r^ 

Prepare  a  solution  of  Hairdo  of  strength  10  mg.  Ir  per  cubic 
centimeter  by  dissolving  the  calculated  amount  (see  Table)  of 
IrCU  in  20  cc.  of  water  containing  dil.  HC1.  Dilute  separate  por- 
tions of  this  solution  with  water  to  give  solutions  of  strength  5, 
2  and  1  mg.  respectively  of  Ir  per  cubic  centimeter. 

1.  Action  of  H2S.     Introduce  into  a  small  beaker  10  cc.  of 
indium  solution  containing  1  mg.  Ir  per  cubic  centimeter.     Add 
2.5  cc.  of  dil.  HC1  and  dilute  the  solution  with  water  to  25  cc. 
Pass  in  H2S.     Note  the  bleaching  of  the  solution  with  the  sepa- 
ration of  sulphur.     Heat  the  mixture  to  boiling  and  again  treat 
with  H2S  for  about  thirty  seconds.     Boil  again  and  pass  in  H2S 
for  a  half  minute.     Repeat  this  process  of  boiling  and  treating 
with  H2S  until  a  brown  precipitate  is  obtained.     Its  formula  is 
Ir2S3.    Note.     Ir2S3  is  soluble  in  (NH4)2S*. 

2.  Action  of  NH4OH.  In  a  test-tube  treat  1  cc.  of  iridium  solu- 
tion containing  2  mg.  Ir  with  1   cc.  of  dil.  NH4OH.     Note  the 
change  in  color  from  brown  to  olive-green.  Note.  NaOH  produces 
the  same  change  in  color. 

3.  Action  of  (NH4)2S.    Treat  in  a  test-tube  2  cc.  of  iridium 
solution  containing  2  mg.  of  Ir  per  cubic  centimeter  with  2  cc. 
of  dil.  NH40H.     Note  the  olive-green  color  of  the  solution.    Pass 
in  H2S  and  observe  that  no  precipitate  forms,  also  that  the  solu- 


28  RARER  ELEMENTS 

tion  assumes  a  darker  color.  Acidify  the  solution  with  dil.  HC1. 
Note  that  the  color  is  bleached.  Heat  the  solution  to  boiling 
and  observe  the  brown  turbidity  which  is  due  to  the  separation  of 
Ir2S3. 

4.  Action  of  NaOH.    To  1  cc.  of  iridium  solution  containing 
5  mg.  Ir,  add  1  drop  of  NaOH  solution.     Note  the  change   in 
color.      Boil  the    solution  and  shake  the  tube  for    a    minute. 
Observe  the  formation  of  an  azure-blue  precipitate. 

5.  Action  of  NH4C1.     In  a  test-tube  treat  1  cc.  of  iridium  solu- 
tion containing  10  mg.  Ir  with  1  g.  of  solid  NH4C1.     Shake  the 
mixture   till   all  is   dissolved.     Continue   the   addition   of   solid 
NH4C1 1  g.  at  a  time  with  shaking  until  an  excess  of  1  g.  is  present. 
Shake  the  mixture  thoroughly.     The  blackish-red  compound  which 
forms  is  (NH4)2IrCl6. 

6.  Action  of  KC1.     Repeat  Exp.   5  using  solid    KC1  instead 
of  NH4C1.     The  brownish-black  precipitate  is  K^IrClo. 

7.  Action  of  Reducing  Agents.  Use  an  iridium  solution  of 
strength  1  mg.  Ir  per  cubic  centimeter  for  these  tests. 

(a)  Oxalic  Acid.    To  1  cc.  of  iridium  solution  add  1  cc.  of 
oxalic  acid  solution.     Boil.     The  bleaching  is  due  to  the  reduction 
of  IrIV  to  Irm. 

(b)  FeSO4.     Treat  1  cc.  of  iridium  solution  with  3  drops  of 
cone.   H2S04  and  0.5  g.  FeS04.    Boil.     Note  that  the  solution  is 
bleached. 

(c)  SnCl2.     In  a  test-tube  add  to  1  cc.  of  iridium  solution,  1  cc. 
of  SnCb.     Note  that  the  color  of  the  solution  is  bleached. 

(d)  Zn+HCl.     In  a  small  evaporating  dish  treat  2  cc.   of 
iridium  solution  with  2  cc.  dil.  HC1.     Add  a  piece  of  zinc  and  note 
the  reduction  to  metallic  Ir. 

Note.  Sodium  formate  in  the  presence  of  a  little  acetic  acid 
slowly  reduces  a  solution  of  IrCl4. 

8.  Glow  Test.    Apply  the  glow  test  to  0.5  cc.  of  iridium   solu- 
tion.    For  procedure  see  Exp.  11  under  Pt. 

GOLD 

Except  where  otherwise  specified,  use  a  solution  of  HAuCl4- 
4H20  of  strength  2  mg.  Au  per  cubic  centimeter. 

1.  (a)  Precipitation  of  AuS.  Introduce  into  a  small  beaker 
5  cc.  of  gold  solution.  Add  2.5  cc.  dil.  HC1.  and  dilute  the  solution 


GOLD  29 

to  a  volume  of  25  cc.  Pass  in  H2S  for  several  minutes.  The  black 
precipitate  is  AuS  or  Au2S2. 

2HAuCl4+3H2S  =  Au2S3+8HCl, 

Au2S3  =  2AuS+S. 

Allow  the  precipitate  to  settle  and  pour  off  the  clear  solution.  Add 
10  cc.  of  water,  stir,  allow  to  settle  and  pour  off  the  water. 

(6)  The  Insolubility  of  AuS  in  HNO3  and  its  Solubility  in 
Aqua  Regia.  Transfer  a  small  portion  of  the  precipitate  to  a 
beaker  and  demonstrate  its  insolubility  in  hot  HNOs.  Now  add 
HC1  and  heat.  Note  that  the  precipitate  dissolves. 

(c)  Solubility  of  AuS  in  K2S2.  To  the  remainder  of  the  pre- 
cipitate of  AuS  in  the  beaker,  add  2  cc.  of  K2S2  solution  and  warm 
gently.  The  solution  which  results  contains  the  gold  as  a  thio  salt. 

2AuS+K2S2  =  2KAuS2. 

Acidify  this  solution  with  dil.  HC1.  The  yellowish-brown  precip- 
itate which  forms  is  a  sulphide,  probably  Au2S3.  A  control  run 
at  the  same  time  with  2  cc.  of  K2S2  will  make  the  last  result  more 
evident. 

Note.  AuS  is  difficultly  soluble  in  (NH4)2SX  hence  K2S2  was 
used  in  the  above  experiment.  From  a  hot  solution  of  gold,  H2S 
gives  a  brown  precipitate  of  finely  divided  gold  which  is  soluble  in 
hot  K2S2  with  the  formation  of  a  thio  salt. 

2.  Action  of  (NH4)2S.     Prepare  some  colorless  (NH4)2S  by 
passing  H2S  for  thirty  seconds  into  5  cc.  of  dil.  NELiOH.     To  1  cc. 
of  gold  solution  add  5  drops  of  (NH4)2S  solution  and  shake  for  a 
few  moments.    The  brownish-black  precipitate  is  AuS.     Now  add 
2  cc.  of  (NH4)2S  in  excess,  shake  the  mixture  and  heat  nearly  to 
boiling.     Note  that  the  precipitate  practically  all  dissolves.    The 
minute  residue,  consisting  of   exceedingly  fine  black  particles  is 
probably  metallic  gold. 

3.  Action  of  NaOH  orKOH.    In  a  test-tube  treat  1  cc.  of  gold 
solution  with  1  drop  of  NaOH  and  observe  that  no  precipitate 
forms.    Note.  In  more  concentrated  solutions,  however,  a  reddish- 
brown  precipitate  of  Au(OH)3  is  formed.     The  precipitate  resem- 
bles Fe(OH)3  in  appearance,  but  differs  from  the  latter  in  the  ease 
with  which  it  dissolves  in  an  excess  of  the  reagent  forming  sodium 
aurate  NaAu02. 


30  RARER  ELEMENTS 

4.  Action  of  NH4OH.    To  1  cc.  of  gold  solution  add  a  little  dil. 
NKUOH.    The  yellow  precipitate  is  a  mixture  of  gold  imino 
chloride  Au(NH)Cl  and  gold  imino  amide  Au(NH)NH2.     This 
mixture  is  also  known  as  fulminating  gold  because  of  its  property 
when  dried  of  exploding  by  warming  or  by  concussion. 

The  following  tests  are  intended  for  the  .detection  of  small 
amounts  of  gold.  In  making  these  tests  use  a  solution  of  gold  of 
strength  0.1  mg.  Au  per  cubic  centimeter. 

5.  Action  of  Oxalic  Acid.    To  3  cc.  of  gold  solution  (see  note 
above)  add  a  few  drops  of  oxalic  acid  solution  and  heat  to  boiling. 
The  precipitate  consists  of  finely  divided  gold  (distinction  from  Pt j . 

2HAuCl4+3H2C2O4  =  2Au+6CO2+8HCl. 

6.  Action  of  SnCl2.     (a)  In  a  test-tube  treat  3  cc.  of  gold  solu- 
tion with  1  cc.  of  cone.  HC1.     From  a  pipette  add  1  drop  of  SnCl2 
solution.     Shake  the  mixture  and  note  the  colloidal  precipitate  of 
gold  which  slowly  forms.     The  precipitate  is  called  Purple  of 
Cassius.     (6)  Repeat  experiment  (a)  using  1  cc.  of  water  in  place 
of  the  cone.  HC1  and  observe  that  a  brown  solution  is  obtained. 

2HAuCl4+3SnCl2=2Au+2HCl+3SnCl4. 

7.  Action  of  Sulphurous  Acid.    To  3  cc.  of  gold  solution  add  1 
drop  of  a  saturated  aqueous  solution  of  SO 2-     Note  the  pink  color 
of  the  resulting  solution.     Warm,  if  necessary  to  bring  out  the 
color. 

2HAuCU  =  2Au+2HCl+6Cl, 
6C1+3H20  =  6HC1+3O, 
3H2S03+30  =  3H2S04. 

8.  Action  of  FeSC>4.     In  a  test-tube  treat  3  cc.  of  gold  solution 
with  a  few  crystals  of  FeSO4.     Observe  that  the  gold  is  precipitated 
in  the  form  of  a  finely  divided  brown  powder. 

9.  Action  of  H2O2  in  NaOH  Solution.     To  3  cc.  of  gold  solution 
add  5  drops  of  NaOH  and  2  cc.  of  3  per  cent  H202.     Shake  for  a 
minute  and  note  the  formation  of  colloidal  gold. 


SELENIUM  31 


SELENIUM 
Reactions  of  Selenious  Compounds 

Use  a  solution  of  H2Se03  of  strength  10  mg.  Se  per  cubic  centi- 
meter. 

1.  Action  of  H2S.     Introduce  into  a  small  beaker  5  cc.  of 
H2SeO3  solution.     Add  2.5  cc.  dil.  HC1  and  dilute  the  solution 
with  water  to  25  cc.     Pass  in  H2S.     The  lemon-colored  precipitate 
which  forms  is  a  mixture  of  Se  and  S.     Heat  to  boiling  and  again 
pass  in  H2S.     Observe  that  the  precipitate  becomes  reddish. 

H2Se03-j-2H2S  =  Se+2S-f3H20. 

Filter  off  the  precipitate  and  wash  it  twice  with  hot  water.  Heat 
3  cc.  of  (NH^Sz  and  pour  the  solution  on  the  filter.  Catch  the 
liquid  which  passes  through  in  a  test-tube,  heat  and  again  pass  it 
through  the  precipitate.  Note  that  the  precipitate  dissolves. 
Acidify  the  (NH^S*  solution  with  dil.  HC1  and  observe  that  the 
lemon-yellow  mixture  reprecipitates. 

2.  Action  of  (NH4)2S.     To  1  cc.  of  H2Se03  solution  add  5  'cc. 
of  dil.  NH40H  and  pass  in  H2S.    Note  the  formation  of  a  reddish- 
brown  solution.     Now  acidify  the  solution  with  dil.  HC1  and  note 
the  precipitation  of  red  Se. 

3.  Action  of  BaCl2  in  Neutral  Solution.    In  a  test-tube  treat 
1  cc.  of  BaCl2  solution  with  3  drops  of  dil.  NH4OH.    Now  add  1 
cc.  of  H2Se03  solution.     The  precipitate  is  BaSe03.      Add  1  cc. 
of  dil.  HC1  and  note  that  the  precipitate  dissolves. 

4.  Action  of  H2S03.    To  1  cc.  of  H2SeO3  solution  add  3  cc.  of 
cone.  HC1.     Add  0.2  g.  anhydrous  Na2S03.     The  red  precipitate  is 
Se. 

5.  Action  of  SnCl2.    Treat  1  cc.  of  H2SeO3  solution  contained 
in  a  test-tube  with  1  cc.  SnCl2  solution.     The  red  precipitate  is  Se. 

6.  Action  of  FeSO4.     Into  a  10  cc.  graduate  introduce  1  cc.  of 
H2SeO3  solution  and  2  cc.  dil.  HC1.     Mix  and  pour  the  mixture 
into  a  clean  test-tube.     Clean  the  graduate  and  mix  in  it  1  cc.  of 
H2SeO3  solution  and  2  cc.  of  cone.  HC1  and  transfer  the  mixed  solu- 
tion to  another  test-tube.     To  each  test-tube  add  0.5  g.  FeSC>4. 
Observe  that  a  red  precipitate  of  Se  immediately  forms  in  the  tube 


32  RARER  ELEMENTS 

containing  the  concentrated  acid  while  none  forms  in  the  other 
tube.  Heat  the  tube  in  which  no  precipitate  forms  to  boiling  and 
note  the  slowly  forming  precipitate. 

Note.  The  action  of  FeS04  or  H2SOa  in  precipitating  Se  from 
selenious  compounds  in  strong  HC1  solution,  may  be  utilized  to 
separate  Se  from  Te  when  present  together  in  solution. 

7.  Action  of  Zn+HCl.  To  1  cc.  of  H2Se03  solution  add  1  cc. 
of  dil.  HC1  and  a  little  Zn.     Note  the  deposition  of  Se  on  the  Zn. 

8.  Action  of  Heat  on  Se.  Dip  the  moistened  end  of  a  glass  rod 
into  some  selenium  and  heat  in  flame.     Note  the  bluish  flame  and 
disagreeable  odor. 

Reactions  of  Selenic  Compounds 

Use  a  solution  of  K2Se04  of  strength  10  mg.  Se  per  cubic  centi- 
meter. 

1.  Action  of  H2S.     (a)  Introduce  into  a  small  beaker  5  cc.  of 
K2SeO4  solution.    Add  2.5  cc.  dil.  HC1  and  dilute  the  solution  with 
water  to  25  cc.     Pass  in  H2S.     Observe  that  no  precipitate  forms 
(distinction  from  selenious  compounds) .     Heat  to  boiling  and  again 
pass  in  H2S.     Note  that  even  on  heating  no  precipitate  forms. 

(6)  Mix  in  a  small  evaporating  dish  5  cc.  of  K2Se04  solution  and 
5  cc.  of  cone.  HC1.  Heat  to  boiling  and  evaporate  the  solution  to 
5  cc.  Transfer  the  solution  to  a  small  beaker.  Dilute  with  water 
to  50  cc.  and  treat  with  H2S.  A  lemon-yellow  precipitate  of  Se 
will  now  be  obtained.  Note.  The  cone.  HC1  reduced  the  H2Se04 
to  HoSeOa  from  which  Se  was  readily  precipitated  by  H2S. 

H2Se04+2HCl  =  H2Se03+H20+2Cl. 

2.  Action  of  BaCl2.     To  1  cc.  of  K2SeC>4  solution  add  1  cc.  of 
dil.  HC1  and  5  drops  of  BaCl2  solution.     Shake  the  mixture. 
The  white  precipitate  is  BaSe04  (distinction  from  selenious  acid). 
Add  2  cc.  of  cone.  HC1  and  boil.     Note  that  the  precipitate  dis- 
solves with  the  evolution  of  chlorine  (distinction  from  BaSCU). 

BaSe04+4HCl  =  BaCl2-f-H2Se03+2Cl+H2O. 

?.  Action  of  H2SOs.  (a)  In  a  test-tube  treat  1  cc.  of  K2Se04 
solution  with  1  cc.  of  cone.  HC1  and  0.2  g.  Na2S03.  Observe  that 


TELLURIUM  33 

no  reduction  takes  place.     Now  heat  the  mixture  and  note  the 
formation  of  a  red  precipitate  of  Se. 

(b)  In  a  small  evaporating  dish  or  test-tube,  boil  down  a  mix- 
ture of  1  cc.  of  K2SeO4  solution  and  1  cc.  of  cone.  HC1  to  1  cc 
Cool.  Add  1  cc.  of  cone.  HC1  and  0.2  g.  Na2S03.  Account  for  the 
difference  in  the  results  obtained  in  (a)  and  (6) . 


TELLURIUM 
Reactions  of  Tellurous  Compounds 

Use  a  solution  of  K2Te03  of  strength  10  mg.  Te  per  cubic 
centimeter. 

1.  Action  of  Dil.  HC1  on  K2TeO3.     To  1  cc.  of  K2Te03  solution 
add  1  drop  of  dil.  HC1.     The  precipitate  is  H2Te03.     Now  add 
several  more  drops  of  dil.  HC1  and  note  that  the  precipitate  dis- 
solves. 

2.  Action  of  H2S.     Introduce  into  a  small  beaker  5  cc.  of 
K2Te03  solution.     Add  2.5  cc.  dil.  HC1  and  dilute  the  solution 
with  water  to  25  cc.     Pass  in  H2S.     The  brown  precipitate  is 
TeS2.     Filter  it  off  and  wash  it  several  times  with  water.     Pass 
twice  through  the  filter  2  cc.  of  warm  (NEU^S*  and  catch  the  solu- 
tion in  a  test-tube.     Observe  that  TeS2  is  soluble  in  (NH^S*. 
Acidify  the  (NEU^Sz  solution  with  dil.  HC1.     The  brown  pre- 
cipitate is  TeS2. 

3.  Action  of  H2SO3.     In  a  10  cc.  graduate  mix  1  cc.  of  K2TeO.j 
solution  with  3  cc.  of  cone.  HC1  and  pour  the  solution  into  a  test- 
tube.     Into  a  second  test-tube  introduce  a  solution  prepared  by 
mixing  1  cc.  of  K2Te03  solution  with  3  cc.  of  dilute  HC1.     To 
each  tube  add  0.2  g.  anhydrous  Na2SO3.     Shake  and  heat  each  to 
boiling.     Note  that  a  black  precipitate  of  Te  forms  only  in  the 
tube  containing  the  dil.  HC1.     What  conclusion  can  you  draw 
from  these  experiments  as  to  the  influence  of  the  concentration  of 
the  HC1  on  the  precipitation  of  Te  by  H2S03?     Does  a  high  con- 
centration of  HC1  interfere  with  the  precipitation  of  Se  (ous)   by 
H2Se03  (see  Exp.  4  under  Se  (ous))?   How  would  you  separate  Se 
from  Te  in  a  solution  containing  both?     Note.     A  white  precip- 
itate of  NaCl  separates  in  the  tube  containing  the  cone.  HC1.    If 
after  boiling,  the  solution  be  diluted  with  water,  a  precipitate  of 
Te  will  be  obtained. 


34  RARER  ELEMENTS 

4.  Action  of  Zn+HCl.     To  1  cc.  of  K2Te03  solution  add  1  cc. 
of  dil.  HC1  and  a  small  piece  of  granulated  Zn.     Note  the  black 
deposit  of  Te  on  the  Zn. 

5.  Action  of  SnCl2.     In  a  test-tube  treat  1  cc.  of  K2TeO3 
solution  with  1  cc.  of  SnCl2.     Note  the  black  precipitate  of  Te. 

6.  Action  of  FeSO4.     Treat  1  cc.  of  K2TeO3  solution  with  2  cc. 
of  dil.  IIC1  and  0.5  g.  FeS04.     Heat  to  boiling  and  note  that  Te 
does  not  precipitate  (distinction  from  Se) . 

7.  Action  of  Magnesia  Mixture.     To  1  cc.  of  K2Te03  solution 
add  1  cc.  of  magnesia  mixture.     Note  the  formation  of  a  white 
precipitate  (distinction  from  Se) . 


Reactions  of  Telluric  Compounds 

Use  a  solution  of  H2Te04-2H20  of  strength  10  mg.  Te  per 
cubic  centimeter. 

1.  Action  of  H2S.     (a)  Introduce  into  a  small  beaker  5  cc.  of 
H2Te04  solution.     Add  2.5  cc.  dil.  HC1  and  dilute  the  solution 
with  water  to  25  cc.     Do  not  heat  the  solution.     Pass  in  H2S. 
Observe   that   no  precipitate  forms  (distinction  from  H2TeO3). 
Now  heat  the  solution  to  boiling  and  pass  in  H2S.      Note  the  slight 
precipitate  which  is  obtained. 

(6)  In  a  small  evaporating  dish  mix  5  cc.  of  H2Te04  solution 
'with  5  cc.  of  cone.  HC1.  Heat  to  boiling  and  evaporate  the  solution 
to  5  cc.  Cool.  Dilute  the  solution  with  water  to  50  cc.  and  treat 
with  H2S.  The  brown  precipitate  which  immediately  forms  is 
TeS2.  Explain  the  results  in  (a)  and  (6). 

2.  Action  of  SnCl2.     In  a  test-tube  treat  1  cc.  of  H2Te(>4 
with  1  cc.  of  SnCl2.     Observe  that  no  reduction  takes  place.     Heat 
the  mixture  to  boiling  and  shake.     The  black  precipitate  is  Te. 

MOLYBDENUM 

Solution  A.  A  stock  solution  of  ammonium  molybdate  of 
strength  100  mg.  Mo  per  cubic  centimeter  may  be  prepared  as 
follows:  In  a  beaker  dilute  14.2  cc.  cone.  NH4OH  with  water  to  a 
volume  of  50  cc.  To  the  resulting  solution  add  with  stirring,  15  g. 
Mo03  (99-100  per  cent)  and  stir  until  nearly  all  the  Mo03  is  dis- 
solved. Dilute  with  water  to  100  cc.,  stir,  and  heat  to  boiling. 
Filter  if  the  solution  is  not  perfectly  clear. 


MOLYBDENUM  35 

Solution  B.  Dilute  10  cc,  of  Solution  A  with  water  to  100  cc. 
Mix  thoroughly.  This  solution  will  have  a  concentration  of  10  mg. 
Mo  per  cubic  centimeter. 

1.  Action  of  H2S.  Introduce  into  a  small  beaker  1  cc.  of 
molybdate  solution  A.  Add  2.5  cc.  dil.  HC1  and  dilute  the  solu- 
tion with  water  to  25  cc.  ;  very  slowly  with  stirring  run  in  H2S  one 
bubble  at  a  time  until  5-10  have  been  introduced.  Note  the  blue 
color  of  the  solution.  Now  pass  in  more  H2S  until  precipitation  is 
complete.  The  brownish-black  precipitate  is  MoSa.  Heat  the 
mixture  to  coagulate  the  precipitate;  filter,  and  wash  it  twice  with 
small  amounts  of  hot  water.  Pour  on  the  filter  2  cc.  of  warm 
(NH4)2Sz  and  catch  the  filtrate  in  a  test-tube.  Note  that  some  of 
the  MoSs  dissolves  in  the  (NH4)2Sa;  yielding  a  solution  of  reddish 
color.  Acidify  this  solution  with  dil.  HC1.  The  precipitate  is 
MoS3. 


4)2S  =  (NH4)2MoS4, 
(NH4)2MoS4+2HCl  =  MoS3+2NH4Cl+H2S. 

2.  Action  of  Dilute  Mineral  Acids  on  Strong  Solutions  of  Alkali 
Molybdates.    To  1  cc.  of  molybdate  solution  A  add  dil.  HC1  drop 
by  drop.     The  white  precipitate  is  H2MoO4.     Now  add  more  dil. 
HC1  and  observe  that  the  precipitate  is  soluble  in  an  excess  of  the 
reagent. 

3.  Action  of  (NH4)2S.     In  a  test-tube  treat  1  cc.  of  molybdate 
solution  B  with  1  cc.  of  (NH4)2S.      Observe  first,  that  no  precip- 
itate forms;  explain.    Second,  that  the  solution  on  standing  for 
five  minutes  takes  on  an  orange-red  color.     Acidify  the  solution 
with  dil.  HC1.     What  is  the  brown  precipitate  which  separates? 
For  equations  see  Exp.  1  above. 

4.  Action  of  Alkali  Phosphate.     To  3  cc.  of  molybdate  solution 
B  add  2  cc.  of  dil.  HNO3.     Add  1  drop  of  Na2HP04  solution,  mix 
thoroughly,  heat,  and  allow  to  stand.     What  is  the  precipitate 
which  forms?     Write  its  formula. 

5.  Action  of  Reducing  Agents,    (a)    SnCl2.     Introduce  into  a 
10  cc.  graduate  1  cc.  of  molybdate  solution  B,  1  cc.  of  dil.  HC1  and 
8  cc.  of  water.     Transfer  the  mixed  solution  to  a  test-tube  and  add  ' 
from  a  pipette  1  drop  of  SnCl2  solution.     Mix  thoroughly  and  note 
the  blue  color. 

(6)  Zn.    To  1  cc.  of  molybdate  solution  B  add  1  cc.  of  dil,  HC1 


36  RARER  ELEMENTS 

and  a  small  piece  of  Zn.  Note  the  successive  changes  in  color 
from  blue  to  green  and  finally  to  brown. 

(c)  KCNS  in  the  Presence  of  a  Reducing  Agent  Such  as 
Zn+HCl  or  SnC^.  In  a  test-tube  treat  1  cc.  of  molybdate  solution 
B  with  1  cc.  of  dil.  HC1  and  1  cc.  of  KCNS  solution.  Observe  that 
the  solution  turns  yellow.  Now  add  a  small  piece  of  Zn.  The 
solution  becomes  carmine-red  because  of  the  formation  of  molyb- 
denum thiocyanate.  The  same  red  compound  is  formed  when  a 
drop  of  SnCl2  is  added  instead  of  Zn. 

Note.  The  deep  red  coloration  is  not  destroyed  by  the  addition 
of  phosphoric  acid  (distinction  from  Fe(CNS)3.).  It  is,  however, 
prevented  from  forming  by  the  presence  of  tartaric  acid  and  other 
organic  acids. 

6.  Formation  of  Permolybdate.    To  1  cc.  of  molybdate  solution 
B  add  1  cc.  of  dil.  NH4OH  and  2  cc.  of  3  per  cent  H202.     The  red 
color  is  due  to  the  formation  of  ammonium  permolybdate. 

7.  Action  of  K4Fe (CN) 6.     In  a  test-tube  treat  1  cc.  of  molybdate 
solution  B  with  1  cc.  of  dil.  HC1  and  a  little  K4Fe(CN)G.     The  red- 
dish-brown precipitate  is  molybdenum  ferrocyanide.     Show  that  it 
is  soluble  in  NH4OH;  also  in  NaOH  (distinction  from  uranyl  and 
cupric  ferrocyanide). 

GROUP  3 

Division  A.  Beryllium,  titanium,  thorium,  zirconium,  colum- 
bium,  tantalum,  uranium,  cerium,  lanthanum,  praseodymium, 
neodymium,  yttrium,  erbium. 

Division  B.    Vanadium. 

BERYLLIUM 

Use  a  solution  of  BeS04  of  strength  2  mg.  Be  per  cubic  centi- 
meter. 

1.  Action  of  NH4OH.     To  2  cc.  BeSO4  solution  add  2  drops  of 
dil*»NH4OH  and  then  2  cc.  in  excess.     The  white  precipitate  is 
Be(OH)2  resembling  in  appearance  Al(OH)s.     Note  that  it  is 
insoluble  in  an  excess  of  the  precipitant.     Now  add  an  excess 
(3  cc.)  of  dil.  HC1  and  observe  that  the  precipitate  dissolves. 

2.  Action  of  NaOH.    Note.    If  the  NaOH  solution  is  not  per- 
fectly clear,  filter  it  through  cotton  before  making  the  following 


BERYLLIUM  37 

experiment.  Treat  2  cc.  of  BeS04  in  a  test-tube  with  2  drops  of 
clear  NaOH  solution  and  then  add  1  cc.  in  excess.  Observe  that 
the  precipitate  which  first  forms  redissolves. 

Be(OH)2+2NaOH  =  Na2BeO2+2H20. 

Transfer  the  solution  to  a  small  beaker,  dilute  with  20  cc.  of  water, 
boil  for  one-half  minute  and  allow  the  beaker  to  stand  for  a  minute. 
Observe  that  Be(OH)2  has  been  reprecipitated. 

3.  Action  of  (NH4)2S.    To  2  cc.  of  BeS04  solution  add  1  cc.  of 
dil.  NH4OH  and  then  pass  in  H2S.     Note  that  the  precipitate 
remains  unchanged  and  that  it  is  insoluble  in  an  excess  of  the 
reagent. 

4.  Action  of  Na2COs.     In  a  test-tube  treat  2  cc.  of  BeS04 
solution  with  one  drop  of  Na2COs  solution.     Now  add  2  cc.  in 
excess  and  filter.     Boil  the  filtrate.     The  precipitate  which  forms 
is  a  basic  beryllium  carbonate. 

5.  Action  of  (NH4)2CO3.     To  2  cc.  of  BeSO4  solution,  add  2 
drops  of  a  saturated  solution  of  (NH4)2C03.     The  precipitate  is 
basic  beryllium  carbonate.     Now  add  5  cc.  in  excess,  shake  vigor- 
ously and  allow  the  tube  to  stand  for  a  minute.     Note  that  the 
precipitate  completely  dissolves.     Pour  the  solution  into  a  small 
beaker  and  boil  for  one  minute.     Note  the  reprecipitation  of 
basic  beryllium  carbonate  (method  of  separation  from  Al  and  Fe). 

6.  Action  of  NaHCO3.     To  5  cc.  of  BeS04  solution  add  0.2  g. 
solid  NaHCOa  and  shake  the  mixture  vigorously.     Note  the  forma- 
tion of  a  precipitate.     Now  add  0.5  g.  of  NaHCOs,  heat  the  mix- 
ture to  boiling,  boil  for  a  few  minutes  and  allow  it  to  stand. 
Observe  that  the  precipitate  completely  dissolves  (method  of  sep- 
arating Be  from  Al,  Fe  and  Ti) . 

7.  Action  of   (NH4)2C2O4   or  H2C2O4.     (a)  Treat   2   cc.   of 
BeS04  solution  with  1  cc.  (NH4)2C204  solution  and  boil.     Note 
that  no  precipitate  forms  (distinction  from  Th,  Zr,  Ce,  Er,  Y,  La, 
Pr  and  Nd).     (6)  Repeat  Exp.  (a)  using  1  cc.  of  oxalic  acid  instead 
of  (NH4)2C2O4.     Note  that  the  result  is  the  same  as  in  (a). 

8.  Action  of  K2SO4.     To  2  cc.  of  BeS04  solution  add  2  cc.  of  a 
saturated  aqueous  solution  of  K2S04.     Shake  vigorougly  and  then 
boil  the  solution.     Observe  that  no  precipitate  forms  (distinction 
from  Zr,  Th,  Ce,  La,  Pr,  and  Nd). 


38  RARER  ELEMENTS 


TITANIUM 

Use  a  solution  of  Ti  (864)2  of  strength  10  mg.  Ti  per  cubic 
centimeter  prepared  as  follows:  Introduce  into  a  small  beaker 
10  cc.  of  cone.  H2SO4.  Add  with  stirring  1  g.  of  Ti02-H20  and 
heat  with  constant  stirring  till  complete  solution  takes  place. 
Pour  contents  of  beaker  cautiously,  a  little  at  a  time,  into  40  cc.  of 
water.  Mix  thoroughly  and  cool. 

1.  Action  of  NH4OH.     To  2  cc.   of  Ti(S04)2  solution  add 
NH4OH  to  alkaline  reaction.     The  white  precipitate  isTi(OH)4. 
Add  an  excess  of  the  reagent  and  note  that  the  precipitate  is  prac- 
tically insoluble  in  excess.      Transfer  a  portion  of  the  suspended 
precipitate  to  another  test-tube  and  add  an  excess  of  cone.  HC1. 
Observe  that  the  precipitate  dissolves.    Note.  With  NaOH,  KOH 
or  (NH4)2S  the  same  compound  is  precipitated.     If  the  solution  is 
hot,  these  reagents  precipitate  metatitanic  acid  H2Ti03  which  is 
difficultly  soluble  in  acids. 

2.  Action  of  Water,  (a)  In  a  beaker  dilute  2  cc.  of  Ti(S04)2 
solution  with  50  cc.  of  water  and  heat  to  boiling.     Note  cloudiness 
due  to  precipitation  of  H4TiO4. 

Ti(S04)2+4H2O^H4TiO4+2H2S04. 

(6)  In  a  beaker  treat  2  cc.  of  Ti(S04)2  solution  with  1  cc.  of 
cone.  H2SO4  and  49  cc.  of  water;  mix  and  heat  the  solution  to 
boiling.  Explain  why  the  solution  remains  clear.  Keep  this 
solution  for  the  next  experiment. 

(c)  To  the  boiling  solution  of  Exp.  2b  above,  add  5  g. 
NaC2H302.  Note  and  account  for  the  precipitate  which  forms. 

Ti(S04)2+4NaC2H302  =  Ti  (C2H302)4+2Na2S04, 
Ti(C2H3O2)4+3H20  =  H2Ti03+4HC2H302. 

3.  Action  of  Na2S2O3.     In  a  test-tube  treat  1  cc.  of  Ti(S04)2 
solution  with  0.2  g.  Na2S2O3  and  boil  the  mixture.     The  precipitate 
consists  of  H2Ti03+S. 

Ti(S04)2+2Na2S203+H20  =  H2Ti03+2Na2S04+2S+2S02. 


TITANIUM  39 

4.  Action  of  H2O2.     (a)  To  1  cc.  of  Ti(SO4)2  solution  add  1  cc. 
of  3  per  cent  H2C>2.     The  orange-red  color  is  due  to  the  formation 
of  Ti02-H2O2. 

(&)  Action  of  H2O2  in  More  Dilute  Solutions.  Dilute  1  cc.  of 
Ti(S04)2  solution  with  water  to  100  cc.  Mix  thoroughly  and  to 
1  cc.  of  this  solution  in  a  test-tube  add  1  cc.  of  3  per  cent  H2O2. 
Observe  the  yellow  coloration.  Note.  Reserve  some  of  the 
dilute  solution  of  Ti(SO4)2  for  Exp.  66. 

Note.  This  test  for  Ti  is  capable  of  detecting  in  HoSCU  solu- 
tion 0.005  per  cent  Ti02  with  certainty;  but  it  is  only  reliable  in 
the  absence  of  cerium,  molybdate,  vanadate  and  chromate  ions. 

5.  Action  of  Reducing  Agents.    ZnorSn.     To  2  cc.  of  Ti(SO4)2 
solution  add  a  piece  of  zinc  and  warm  the  mixture  gently.     The 
violet  color  which  develops  is  due  to  the  formation  of  Ti2 (804)3 • 
Note.     Neither  H2S  nor  H2SOs  reduces  tetravelant  Ti  (distinc- 
tion from  ferric  ion). 

6.  Action  of  Cupferron.     (The  NH4  salt  of  phenyl-nitrosohy- 
droxylamine  C6H5NO  •  NONH4)  (a)  To  2  cc.  of  Ti(S04)2  solution 
add  1  cc.  of  a  6  per  cent  aqueous  solution  of  cupferron.     The  yellow 
precipitate  is  Ti(C6H5NONO)4.     (6)  To  5  cc.  of  the  dilute  Ti 
solution  reserved  in  Exp.  4b  add  1  cc.  of  cupferron  solution.     Ob- 
serve the  formation  of  a  yellow  precipitate. 

Note.  Ferric  ions  give  a  red  precipitate  with  this  reagent.  To 
test  for  Ti  in  solutions  containing  Fe,  proceed  as  follows:  To  the 
acid  solution  add  H2C4H40o  in  amount  equal  to  about  four  times 
the  weight  of  Ti  and  Fe  present.  Treat  with  H2S  till  all  the  Fe 
is  reduced.  Then  precipitate  the  Fe  as  FeS  by  making  the  solution 
alkaline  with  NB^OH  and  treating  again  with  H^S.  Filter  off 
the  FeS,  acidify  the  filtrate  with  H2S04,  boil  to  expel  the  H2S 
and  finally  precipitate  the  Ti  with  cupferron. 

7.  Action  of  K4Fe(CN)6.     To  2  cc.  of  Ti(SO4)2  solution  add  1  cc. 
of  K4Fe(CN)e  solution.     Shake  the  tube  for  a  minute  and  observe 
the  formation  of  a  brown  precipitate. 

8.  Action  of  Na2HPO4.     In  a  test-tube  treat  2  cc.  of  Ti(S04)2 
solution  with  1  cc.  of  Na2HP04  solution  and  shake  the  mixture  for  a 
minute.  The  white  precipitate  is  basic  titanic  phosphate  TiOHPO4. 


40  RARER  ELEMENTS 


THORIUM 

Use  a  solution  of  Th(N03)4  of  strength  10  mg.  Th  per  cubic 
centimeter. 

1.  Action  of  NH4OH.     To  2  cc.  of  thorium  solution  add  2 
drops  of  dil.  NH4OH  and  then  add  2  cc.  in  excess.     The  white 
precipitate  is  Th(OH)4.     Note  that  it  is  insoluble  in  excess  of  the 
reagent.     Now  add  an  excess  (3  cc.)  of  dilute  HC1  and  observe 
that  the  precipitate  dissolves. 

2.  Action  of  NaOH.     Repeat  Exp.   1  using  NaOH  instead  of 
NH4OH.     Note  that  Th(OH)4  is  insoluble  in  excess  of  NaOH. 

3.  Action  of  (NH4)2S.     In  a  test-tube  treat  2  cc.  of  thorium 
solution  with  1  cc.  of  dil.  NH4OH.     Treat  the  mixture  with  H2S. 
Note  that  the  Th(OH)4  remains  unchanged  and  is  insoluble  in  an 
excess  of  the  precipitatant. 

4.  Action  of  Na2CO3.  To  2  cc.  of  Th(N03)4  solution  add  2 
drops  of  Na2COs  solution  and  then  2  cc.  in  excess.     Note  that  the 
carbonate  which  first  forms  is  soluble  in  an  excess  of  the  reagent. 
Heat  the  solution   to   boiling  and  observe   that   reprecipitation 
takes  place.     To  the  precipitate  in  the  tube  add  an  excess  of  dil. 
HC1  and  observe  that  the  precipitate  completely  dissolves. 

5.  Action  of  K2SO4.     To  2  cc.  of  Th(NO3)4  solution  add  2  cc. 
of  a  saturated  aqueous  solution  of  K2SO4.     Shake  the  tube  vigor- 
ously for  a  minute  and  allow  it  to  stand  for  two  minutes.     The 
crystalline  precipitate  which  forms  is  a  double  sulphate  of  Th  and  K 
having  the  formula  Th(S04)2-2K2S04-2H20   (distinction  from 
Al,  Be,  and  Yttria  earths).    Add  2  cc.  of  K2S04  in  excess  and 
observe  that  the  precipitate  does  not  dissolve.     Note.     The  corre- 
sponding Na  salt  is  soluble  in  water  as  well  as  in  a  saturated  solu- 
tion of  Na2SO4. 

6.  Action  of  Oxalic  Acid.     Treat  2  cc.  of  Th(N03)4  solution 
with  1  cc.  of  H2C2O4  solution.     The  white  crystalline  precipitate 
is  Th(C204)2  •  6H2O.    Divide  the  precipitate  into  2  equal  portions. 
To  one  add  2  cc.  more  of  the  reagent.      To  the  other  add  5  cc.  dil. 
HC1.     Observe  that  the  precipitate  is  practically  insoluble  in  an 
excess  of  either  reagent. 

7.  Action  of  (NH4)2C2O4.     (a)  To  2  cc.  of  Th(N03)4  solution 
add  1  cc.  of  (NH4)2C2O4  solution.     The  precipitate  is  Th(C2O4)2 
(distinction  from  Al  and  Be).     Add  3  cc.  of  (NH4)2C204  in  excess 


THORIUM  41 

and  boil  the  mixture.  The  solubility  of  the  precipitate  in  an 
excess  of  the  reagent  is  due  to  the  formation  of  a  double  oxalate  of 
NH4  and  Th.  To  the  clear  solution  add  1  cc.  of  dil.  HC1.  Note 
that  Th(C204)4  is  reprecipitated  (distinction  from  Zr).  (6)  Pre- 
pare some  Th(C204)2  as  directed  in  (a).  Add  5  cc.  of  NEL^HsC^ 
solution  and  boil  the  mixture.  Note  that  the  precipitate  dissolves. 
Now  add  3  cc.  dil.  HC1  and  note  the  reprecipitation  of  Th(C204)2. 
(c)  Prepare  some  Th(C204)2  as  directed  in  (a).  Add  5  cc.  dil.  HC1 
and  shake  the  mixture.  Note  that  the  precipitate  is  not  readily 
soluble. 

8.  Action  of  Na2HPO4.     In  a  test-tube  treat  2  cc.  of  Th(N03)4 
solution   with   0.5    cc.    Na^HPCU   solution.     The   precipitate   is 
Th3(P04)4-4H20. 

9.  Action  of  KF.    To  2  cc.  of  thorium  solution  add  1  cc.  of  KF 
solution.     Note  the  gelatinous  precipitate  that  forms.      Set  the 
tube  aside  for  one-half  hour  and  observe  that  the  precipitate 
becomes  granular. 

10.  Action  of  K4Fe(CN)6.     Treat  2  cc.  of  thorium  solution 
with  a  little  K4Fe(CN)o.     Note  the  formation  of  a  white  precip- 
itate. 

11.  Action  of  Na2S2O3.     In  a  test-tube  treat  2  cc.  of  Th(N03)4 
solution  with  0.2  g:  Na2S203  •  5H2O  and  boil  the  solution.     The 
precipitate  is  a  mixture  of  Th(OH)4  and  a  basic  thiosulphate 
admixed  with  sulphur   (distinction  from  Ce  and  Yttria  earths 
except  Sc) . 

12.  Action  of  H2O2.     To  2  cc.  of  Th(NO3)4  solution  add  1  cc. 
of  3  per  cent  H202  and  heat.     Note  the  white  gelatinous  precip- 
itate which  forms  (distinction  from  Zr) . 

13.  Action  of  Metanitrobenzoic  Acid.     In  a  test-tube  treat 
2  cc.  of  Th(NO3)4  solution  with  2    cc.  of  a  0.4  per  cent  aqueous 
solution    of    metanitrobenzoic    acid.     The    white    precipitate    is 
thorium  metanitrobenzoate   (distinction  from  Ce,   La,   Pr,   and 
Nd). 

ZIRCONIUM 

Use  a  solution  of  ZrOCl2,  8H20  of  strength  10  mg.  Zr  per  cubic 
centimeter. 

1.  Action  of  NH4OH.  To  2  cc.  of  zirconium  solution  add  2 
drops  of  dil.  NEUOH  and  then  1  cc.  in  excess.  Observe  that  the 


42  RARER  ELEMENTS 

flocculent  precipitate  of  Zr(OH)4  is  insoluble  in  an  excess  of  the 
reagent.  Add  to  the  precipitate  in  the  tube  an  excess  (3  cc.)  of  dil. 
HC1  and  shake  the  mixture  vigorously.  Note  that  the  precipitate 
dissolves. 

2.  Action  of  NaOH.  (a)  In  a  test-tube  treat  2  cc.  of  zirconium 
solution  with  2  drops  of  NaOH  solution  and  then  add  1    cc.    in 
excess.     Note  that  the  precipitate  is  insoluble  in  excess  (distinc- 
tion from  Be  and  Al).     To  the  precipitate  add  5  cc.  dil.  HC1. 
Shake  the  mixture  and  allow  the  tube  to  stand  for  a  few  moments. 
Note  that  the  precipitate  completely  dissolves. 

(6)  To  2  cc.  of  zirconium  solution  add  1  cc.  of  NaOH  solution 
and  boil  the  suspended  precipitate.  Now  add  5  cc.  of  dil.  HC1 
and  shake  the  mixture.  Note  that  the  precipitate  does  not  dis- 
solve readily. 

3.  Action  of  (NH^S.     Treat  2  cc.  of  zirconium  solution  in  a 
test-tube  with  1  cc.  of  dil.  NH40H.     Pass  H2S  into  the  mixture. 
Observe  that  the  precipitate  remains  unchanged  and  that  it  is 
insoluble  in  excess  of  the  reagent.     Note.    The  sulphide  cannot  be 
formed  in  the  wet  way. 

4.  Action  of  (NH^COs.     To  2  cc.  of  zirconium  solution  add  1 
drop  of  (NH^COs  and  shake  the  mixture.     The  flocculent  precip- 
itate which  forms  is  basic  zirconium  carbonate  (3Zr02  •  CO2  *  8H2O) . 
Now  add  5  drops  in  excess  and  observe  how  readily  the  precipitate 
dissolves  in  excess  (distinction  from  Al) .     Boil  the  solution  for  one- 
half  minute.     The  substance  which  precipitates  is  Zr(OH)4. 

5.  Action  of  Na2COs.     (a)  Treat  3  cc.  of  zirconium  solution 
with  one  drop  of  Na2C0.3  solution.     Note  the  formation  of  a  pre- 
cipitate.    Now  add  3  drops  in  excess  and  shake  the  mixture. 
Observe  that  the  precipitate  dissolves  in  excess  (distinction  from 
Al).     Boil   the  solution.     The   substance   which   precipitates   is 
Zr(OH)4. 

(6)  To  3  cc.  of  zirconium  solution  add  1  drop  of  Na9CO3  solu- 
tion and  then  add  3  drops  in  excess.  Shake  the  tube  till  solution 
takes  place.  To  the  clear  solution  add  2  cc.  dil.  NILtOH.  The 
precipitate  is  Zr(OH)4. 

6.  Action  of  Oxalic  Acid,     (a)  To  2  cc.  of  zirconium  solution 
add  1  drop  of  oxalic  acid.     The  white  precipitate  is  zirconium 
oxalate.     Now  add  4  drops  in  excess  and  observe  that  the  pre- 
cipitate is  readily  soluble  in  excess. 

(b)  Prepare  some  zirconium  oxalate  by  adding  1  drop  of  oxalic 


ZIRCONIUM  43 

acid  to  2  cc.  of  zirconium  solution.  Divide  the  precipitate  into  2 
equal  portions.  To  one  add  3  cc.  of  dil.  HC1  and  observe  that  the 
precipitate  does  not  readily  dissolve.  To  the  other  portion  add 
1  cc.  (NH4)2C204  solution.  Note  that  the  precipitate  readily 
dissolves. 

7.  Action  of  (NH4)2C2O4.     (a)  In  a  test-tube  treat  2  cc.  of 
zirconium  solution  with  2  drops  of  (NH4)  2^0^  solution  and  then 
add  5  drops  in  excess.     Observe  that  the  precipitate  of  Zr (0204)2 
readily  dissolves  in  excess.     To  the  clear  solution  add  1  cc.  of  dil. 
NH4OH.     The  precipitate  is  Zr(OH)4. 

(6)  To  2  cc.  of  zirconium  solution  add  2  drops  of  (NH*)fiC/2O4 
solution  and  then  1  cc.  in  excess.  Observe  that  the  precipitate 
dissolves  readily  in  excess.  To  the  clear  solution  add  1  cc.  of  dil. 
HC1.  Repeatedly  filter  through  a  double  filter  if  any  precipitate 
forms  (see  note  below)  until  a  clear  filtrate  is  obtained.  To  the 
latter  add  NH4OH  to  alkaline  reaction. 

Note.  From  an  (NH4)2C20-i  solution  of  zirconium  oxalate, 
HC1  fails  to  reprecipitate  Zr(C204)2  (distinction  from  Th).  The 
solution  was  filtered  in  Exp.  76  because  of  the  presence  of  some 
impurity  in  the  zirconium  solution.  The  relatively  large  precip- 
itate finally  obtained  with  NH^OH  in  the  filtrate  shows  that  prac- 
tically all  of  the  Zr  remained  in  solution  on  adding  the  HC1. 

8.  Action  of  NaoHPO4.     Treat  2  cc.  of  zirconium  solution  with 
5  cc.  of  dil.  H2S04.     Mix  well  and  then  add  1  cc.  of  Na2HPO4. 
The   precipitate   is   a   basic   phosphate   possessing   the   formula 
Zr(OH)PO4.     (Distinction  from  Fe,  Ti,  and  Cr). 

9.  Action  of  K4Fe(CN)G.     To  2  cc.  of  zirconium  solution  add  a 
few  drops  of  K4Fe(CN)e  solution.     Note  the  white  precipitate 
of  ZrFe(CN)6  which  forms. 

10.  Action  of  H2O2.     (a)  Treat  2  cc.  of  zirconium  solution 
with  1  cc.  of  3  per  cent  H202.     Observe  that  no  precipitate  forms. 

(6)  Repeat  experiment  (a)  using  1  cc.  of  30  per  cent  H2O2. 
Note  that  no  precipitate  forms. 

Note.  Working  with  more  concentrated  solutions  of  Zr,  the 
author  was  unable  to  get  a  precipitate  either  with  the  dilute  or 
concentrated  peroxide.  Heating  the  mixed  solutions  or  allowing 
them  to  stand  for  hours,  also  failed  to  induce  precipitation.  These 
obsrvations  are  at  variance  with  the  statement  made  by  Fresen- 
ius,  Tread  well-Hall,  Herzfeld  and  Korn,  and  Classen,  that 
zirconium  solutions  may  be  precipitated  by  HoO2. 


44  RARER  ELEMENTS 

11.  Action  of  K2SO4.    To  2  cc.  of  zirconium  solution  add  3  cc. 
of  a  saturated  aqueous  solution  of  KaSQ*.     Shake  the  tube  vigor- 
ously for  a  minute  and  allow  it  to  stand  for  five  minutes.     The 
white  precipitate  is  a  double  sulphate  of  K  and  Zr.    It  is  insoluble 
in  an  excess  of  the  reagent  (distinction  from  Al  and  Be  and  Yttria 
earths).     To  the  precipitate  in  the  test-tube  add  5  cc.  dil.  HCL 
shake  the  mixture  vigorously  and  allow  it  to  stand  for  a  minute 
or  two.     Note  that  the  precipitate  dissolves. 

12.  Action  of  Turmeric  Solution.     In  a  10  cc.  graduate  mix  1  cc. 
of  water,  1  cc.  of  dil.  HC1,  5  cc.  of  methyl  alcohol  and  1  cc.  of  an 
alcoholic  solution  of  turmeric.     Transfer  the  mixed  solution  to  a 
test-tube.     This  is  the  control  or  blank.     Clean  the  graduate  and 
in  it  measure  1  cc.  of  zirconium  solution,  1  cc.  dil.  HC1,  5  cc.  of 
methyl  alcohol  and  1  cc.  of  turmeric  solution.     Mix  well  and  pour 
the  solution  into  another  clean  test-tube.     Compare  the  tubes  and 
observe  that  the  blank  is  light  yellow  while  the  solution  in  the  tube 
containing  the  Zr  is  reddish-brown. 

13.  Action  of  HF.     To  2  cc.  of  zirconium  solution  in  a  platinum 
crucible,  add  2  cc.  of  48  per  cent  HF.     Stir  the  solution  with  a 
hard  rubber  stirring  rod  and  note  the  absence  of  precipitation 
(distinction  from  Th,  Ce  and  Y,  each  of  which  under  the  same  con- 
ditions gives  a  precipitate). 

14.  Action  of  Na2S2Os.      To  2  cc.  of  zirconium  solution  add  0.2 
g.  of  Na2S203,  and  heat  to  boiling;  the  precipitate  is  Zr(OH)4+S, 
(Method  of  separation  from  Ce  and  distinction  from  Y,  Pr  and 
Nd). 

15.  Action  of  H^SOs.     In  a  test-tube  treat  2  cc.  of  zirconium 
solution  with  2  drops  of  dil.  HC1  and  2  cc.  of  a  saturated  aqueous 
solution  of  S02.    Heat  to  boiling.     The  precipitate  is  Zr(OH)4. 
(Baskerville's  method  of  separating  Zr  from  Fe  and  Al.) 


COLUMBIUM  OR  NIOBIUM 

1.  Solubility  of  Cb2Os  in  HF  and  the  Preparation  of  a  Solution 
of  Columbium.  Into  a  platinum  crucible  introduce  30  mg.  Cb205 
(equivalent  to  20  mg.  CD).  Add  2  cc.  of  48  per  cent  HF  and  heat 
gently  under  hood  on  a  sand  bath  or  asbestos  board.  Note 
that  the  oxide  completely  dissolves.  Cool,  add  2  cc.  of  cone.  H2S04 
and  evaporate  till  SOs  fumes  are  given  off  copiously.  This  is  to 


COLUMBIUM  OR  NIOBIUM  45 

make  sure  that  all  the  HF  has  been  removed.  (If  the  solution  has 
a  dark  color  indicating  the  presence  of  organic  matter,  cool  the 
solution,  add  1  cc.  of  cone.  HNOs  and  evaporate  again  to  SOs 
fumes.)  Note  that  the  EbSCU  solution  is  perfectly  clear.  Cool 
thoroughly.  To  5  cc.  of  cold  water  in  a  small  beaker  add  the  con- 
tents of  crucible,  a  little  at  a  time  with  stirring.  Note  that  the 
diluted  solution  is  perfectly  clear.  This  will  not  be  the  case  if 
larger  amounts  of  Cb  are  used  or  if  the  solution  is  allowed  to 
get  hot. 

2.  Action  of  Zn+HCL   Introduce  2  cc.  of  the  columbium  solu- 
tion prepared  above  into  a  test-tube.     Add  2  cc.  dil.  HC1  and  0.5  g. 
granular  zinc.     Note  the  dirty  blue  color  which  develops  at  the 
end  of  about  one-half  minute  (distinction  from  Ta). 

3.  Action  of  NHiOH.     To  the  remainder  of  the   columbium 
solution  add  cone.  NH^OH  to  alkaline  reaction.     The  white  pre- 
cipitate is  columbic  or  niobic  acid.    Add  dil.  HC1  to  acid  reaction 
and  then  2  cc.  in  excess.     Note  that  the  precipitate  is  insoluble 
in  dil.  HC1.     Reserve  this  mixture  for  the  following  experiment. 

4.  Action  of  H2C>2  on  Columbic  Acid  in  the  Presence  of  HC1. 
To  the  mixture  of  columbic  acid  and  dil.  HC1,  add  5  cc.  3  per  cent 
H202  and  heat  to  boiling.     Note  that  complete  solution  takes 
place.     Reserve  this  solution  for  the  following  experiments. 

5.  Action  of  NH4OH  on  the  H2O2  Solution  of  Columbic  Acid. 
(a)  Render  alkaline  with  NEL^OH  1  cc.  of  the  EkCb  solution  ob- 
tained in  Exp.  4.     Note  that  no  precipitation  takes  place. 

(b)  To  1  cc.  of  the  H202  solution  of  columbic  acid,  add  1  cc.  of 
EbSOa  and  then  render  the  solution  alkaline  with  NH^OH. 
Note  that  precipitation  now  takes  place.  Note.  In  the  above 
experiment  the  H^SOs  destroyed  the  H^C^.  The  H2O2  may  also 
be  removed  by  adding  £[2864  and  evaporating  the  solution  to 
SOs  fumes. 

6.  Action  of  Cone.  H2SO4  on  the  H2O2  Solution  of  Columbic 
Acid.     Pour  into  an  evaporating  dish  the  remainder  of  the  KbC^ 
solution  reserved  in  Exp.  4.     Add  2  cc.  of  cone.  EbSCU  and  evap- 
orate the  solution  to  SOs  fumes.     Cool.     Add  5  cc.  of  cold  water 
and  stir  till  a  uniform  solution  results.     Divide  the  solution  into 
two  portions.     To  the  first  in  a  test-tube  add  2  cc.  dil.  HC1  and 
0.5  g.  zinc.     Note  the  blue  color  which  develops  at  the  end  of 
thirty  seconds.     Make  the  other  portion  alkaline  with  NHiOH 
and  note  the  precipitation  of  columbic  acid.    Pass  H2S  into  the 


46  RARER  ELEMENTS 

suspension  of  columbic  acid  and  note  that  the  precipitate  remains 
unchanged. 

TANTALUM 

1.  Preparation  of  Potassium  Tantalate  Solution.   In  a  platinum 
crucible  mix  125  mg.  of  T^Oo  (equivalent  to  100  mg.  Ta)  with  1  g. 
anhydrous  K^COs.     Cover  the  crucible  and  heat  it  with  a  Meeker 
burner  till  no  more  CO2  is  given  off  and  until  the  melt  is  perfectly 
transparent.      Cool.      Treat  the  melt  in  the    crucible  with    10 
cc.  of  water,  and  stir  until  the  melt  is  completely  dissolved;  then 
dilute  the  solution  with  water  to  20  cc.      If  the  resulting   well- 
mixed  solution  is  not  perfectly  clear,  filter  it  and  use  the  clear 
solution  for  the  following  experiments. 

2.  Action  of  Mineral  Acids,  (a)  To  2  cc.  of  the  tantalum  solu- 
tion add  1  cc.  of  dil.  HC1  and  shake  the  mixture.     The  precipitate 
is  tantalic  acid  HsTaCU. 

(6)  In  a  10  cc.  graduate  measure  3  cc.  dil.  HC1.  Quickly  add 
the  acid  to  2  cc.  of  tantalum  solution  and  shake  the  mixture. 
Note  that  the  precipitate  which  first  forms  redissolves  yielding 
either  a  perfectly  clear  solution  or  one  with  a  faint  opalescence. 
Heat  the  solution  to  boiling  and  note  that  a  precipitate  does  not 
form.  Now  add  1  cc.  dil.  £[2864  and  observe  that  the  solution 
becomes  cloudy.  Heat  to  boiling  and  note  precipitation. 

(c)  To  2  cc.  of  tantalum  solution  add  1  cc.  dil.  HoS04,  shake 
and  note  the  formation  of  a  precipitate. 

(d)  To  2  cc.  of  tantalum  solution  add  quickly  3  cc.  of  dilute 
H2SO4.     Note  that  only  a  faint  cloud  forms.     Heat  the  solution 
to  boiling  and  observe  that  precipitation  takes  place.     Compare  the 
results  obtained  in  (d)  and  (6).     Note.     The  action  of  HNOs  on 
potassium  tantalate  is  the  same  as  that  of  HC1. 

3.  Action  of  NH4OH  and  (NH4)2S.     (a)  To  2  cc.  of  tantalum 
solution  add  quickly  3  cc.  dil.  HC1.      Now   make   the   solution 
alkaline  with  cone.  NHiOH.     The  precipitate  is  tantalic  acid. 
(b)  Treat  the  suspended  precipitate  with  H2S  and  observe  that  the 
precipitate  remains  unchanged. 

4.  Action  of  H2O2  on  Freshly  Precipitated  Tantalic  Acid  in 
the  Presence  of  HC1.    To  4  cc.  of  tantalum  solution  contained  in  a 
small  beaker,  add  quickly  6  cc.  of  dil.  HC1  and  stir  the  solution 
vigorously.    To  the  slightly  turbid  solution  add  cone.    NEUOH 


TANTALUM  47 

to  alkaline  reaction.  Allow  the  precipitate  of  tantalic  acid  to 
settle  and  carefully  pour  off  most  of  the  clear  solution.  Now  add 
dil.  HC1  to  acid  reaction  and  then  2  cc.  in  excess.  Note  the  insol- 
ubilit}^  of  the  precipitate  in  an  excess  of  HC1.  Add  5  cc.  3  per  cent 
H202,  heat  the  mixture  to  boiling  and  stir  it  vigorously.  Note 
that  the  precipitate  does  not  completely  dissolve  (distinction  from 
Cb).  To  show  that  some  of  the  tantalic  acid  has  gone  into  solu- 
tion, filter  off  the  precipitate.  Make  the  filtrate  alkaline  with 
cone.  NH4OH,  and  boil  it  down  to  one-half  of  the  bulk.  Add  2  cc. 
of  H2SOs,  boil  again  to  expel  the  excess  of  862  and  then  make  the 
solution  alkaline  with  NEUOH.  Boil  the  solution  and  note  the 
precipitation  of  HsTaCU. 

5.  Action  of  Zn+HCl.     To  2  cc.  of  tantalum  solution,  quickly 
add  3  cc.  dil.  HC1.     Add  0.5  g.  granulated  zinc  and  allow  the  action 
to  continue  for  several  minutes.     Note  the  absence  of  a  blue 
coloration  (distinction  from  Cb) . 

6.  Action  of  KF  on  the  Fluorides  of  Cb  and  Ta.  Into  a  plat- 
inum crucible  (note  its  number)  introduce  25  mg.  TaoOs.     Into 
another  platinum  crucible  put  30  mg.  Cb205.     To  each  add  1  cc. 
of  cone.  HNOs  and  about  2  cc.  of  48  per  cent  HF.     Place  the  cru- 
cibles on  a  sand  bath  or  on  an  asbestos  board  and  evaporate  the 
solutions  under  a  hood  to  dry  ness.     Cool.     Add  about  1  cc.  of 
48  per  cent  HF  to  each  and  agitate  each  till  complete  solution 
takes  place.     Now  add  to  each  0.5  g.  K^COs  (using  small  portions 
at  a  time  to  minimize  loss  by  spattering) .     The  crystalline  precip- 
itate which   forms  in  the  crucible    containing  jthe  tantalum  is 
K^TaFy.     Note  that  no  precipitate  forms  in  the  crucible  containing 
the  columbium  (method  of  separating  Cb  from  Ta) . 


URANIUM 
Reactions  of  Uranyl  Salts 

Use  a  solution  of  U02(N03)2  of  strength  10  mg.  U  per  cubic 
centimeter. 

1.  Action  of  HoS.  Introduce  into  a  small  beaker  2  cc.  of 
uranium  nitrate  solution.  Add  2.5  cc.  dil.  HC1  and  dilute  the 
solution  to  25  cc.  Pass  in  H2S.  Note  the  absence  of  a  precip- 


48  RARER  ELEMENTS 

itate.     Heat  the  solution  to  boiling  and  treat  again  with 
Observe  that  no  precipitation  takes  place. 

2.  Action  of  NH4OH.     To  2  cc.  of  uranium  nitrate  solution 
add  1  drop  of  dil.  NH4OH.     The  yellow  amorphous    precipitate 
is  ammonium  uranate  (NH4)2U207.     Add  2  cc.  dil.  NH4OH  in 
excess  and  observe  that  the  precipitate  is  insoluble  in  excess. 
Dilute  the  mixture  with  an  equal  volume  of  water,  mix  thor- 
oughly and  divide  the  suspended  precipitate  into  two  equal  por- 
tions.    To  one,  add  10  drops  of  a  saturated  aqueous  solution  of 
H2C4H4Oe.     To  the  other  add  1  cc.  of  a  saturated  solution  of 
(NH4)oCO3.     Observe  that  in  each  case  the  precipitate  dissolves. 

3.  Action  of  NaOH.     Treat  2  cc.  of  uranium  nitrate  solution 
with  one  drop  of  NaOH  solution  and  then  add  1  cc.  in  excess. 
The  yellow  precipitate  is  Na2U207.     Note  that  it  is  insoluble  in 
excess  of  the  reagent. 


Now  add  3  cc.  of  3  per  cent  H202  and  mix  thoroughly.     Note  that 
the  precipitate  dissolves  forming  a  deep  yellow  solution. 

4.  Action  of  (NH.i)2S.    To  2  cc.  of  uranium  nitrate  solution  in  a 
test-tube  add  2  cc.  of  dil.  NH4OH.     What  is  the  yellow  precipitate 
which  forms  (see  Exp.  2)?     Now  pass  in  H2S  for  one-half  minute 
and  observe  the  change  in  the  color  of  the  precipitate  from  yellow 
to  chocolate  brown,  due  to  the  formation  of  UOoS.     Divide  the 
mixture  into  two  equal  portions.     To  one  add  an  equal  volume  of 
dil.  HC1.     To  the  other  add  an  equal  volume  of  (NH4)oCO3  and 
warm  the  mixture.     Note  that  the  precipitate  dissolves  in  each 
case. 

5.  Action  of  (NH4)2CO3.     (a)  In  a  test-tube  treat  2  cc.  of 
uranium  nitrate  solution  with  1  drop  of  (NH4)2C03  solution  and 
shake  the  tube  for  about  a  minute.     The  precipitate  is  a  double 
salt  of  (NH4)2C03  and  (UO2)CO3.     Now  add  (NH4)2CO3  drop 
by  drop  with  shaking  until  the  precipitate  dissolves.      Boil  down 
the  solution  in  an  evaporating  dish  to  about  one-half  the  original 
volume  and  note  the  precipitation  of  (NH4)2U207. 

(b)  The  Precipitation  of  Na2U2O7  from  an  (NH4)2CO3  Solu- 
tion of  Uranium.  To  2  cc.  of  uranium  nitrate  solution  add  1  drop 
of  (NH4)2C03  and  shake  till  precipitation  takes  place.  Now  add 
(NH4)2C03  (1  drop  at  a  time  with  shaking)  till  a  clear  solution 


URANIUM  49 

results.     To  the  clear  solution  add  a  little  NaOH.     The  precip- 
itate is  Na2U207. 

6.  Action  of  Na2CC>3.     In  a  test-tube  treat  2  cc.  of  uranium 
nitrate  solution  with  1  drop  of  Na2COs  solution  and  shake  the 
solution  for  a  minute.     Observe  that  no  precipitate  forms.     Note. 
In  more  concentrated  solutions,  e.g.,  one  containing  100  mg.  U 
per     cc.,    a    precipitate     of   sodium    uranyl    carbonate   forms 
2Na2C03-UO2C03.     This  precipitate  is  moderately  soluble  in 
water,  hence  it  does  not  form  in  dilute  solutions.     It  is  soluble  in 
an  excess  of  Na2COs  but  more  readily  in  NaHCOs  solution.     To 
the   above  solution  in  the  tube  add  NaOH  and  note  the  pre- 
cipitation of  Na2Uo07. 

7.  Action  of  H2O2.     To  2  cc.  of  uranium  nitrate  solution  add  3 
drops  of  3  per  cent  H202.     The  white  gelatinous  precipitate  is 
hydrated  uranium  tetroxide  U04.     Now  add  3  or  4  drops  of 
Na2COs  solution  and  note  that  the  precipitate  dissolves  with  the 
formation   of  a  reddish-yellow  solution.     The  colored  compound 
is  said  to  be  uranyl   sodium  peruranate  having  the  formula 
(U02)Na2U208  (J.  Aloy). 

8.  Action  of  K4Fe(CN)e.    Treat   2   cc.   of  uranium   nitrate 
solution  with  a  few  drops  of  K4Fe(CN)e.     The  reddish-brown  pre- 
cipitate is   (U02)2Fe(CN)6.     Divide  the   suspended   precipitate 
into  three  equal  portions.     To  the  first  portion,  add  a  few  drops  of 
NaOH.     Note  that  the  precipitate  becomes  yellow  due  to  the  for- 
mation of  Na2U2O?  (distinction  from  the  corresponding  copper 
compound). 


Treat  the  second  portion  with  2  cc.  dil.  HC1  and  heat  the  mixture 
to  boiling.  Observe  that  the  precipitate  dissolves  with  the  forma- 
tion of  a  yellow  solution.  To  the  third  portion,  add  2  cc.  (NH^COs 
solution  and  warm  the  mixture.  Note  that  a  clear  yellow  solution 
results. 

9.  Action  of  Na2HPO4.  To  2  cc.  of  uranium  nitrate  solution 
add  a  little  Na2HP04  solution.  The  yellowish-white  precipitate 
is  U02HPO4-#H20.  On  separate  small  portions  of  the  precip- 
itate try  the  action  of  dil.  HC1  and  of  HC2Hs02.  Note.  In  the 
presence  of  NH4  salts,  yellowish-white  ammonium  uranyl  phos- 
phate NH4(U02)P04-zH2O  is  thrown  down.  This  precipitate 


50  RARER  ELEMENTS 

like  the  one  above  is  insoluble  in  acetic  but  soluble  in  mineral 
acids. 

10.  Action  of  Zn+HCl.  In  a  test-tube  treat  2  cc.  of  uranium 
nitrate  solution  with  1  cc.  of  cone.  HC1  and  a  piece  of  zinc.  Warm 
the  mixture  and  allow  the  action  to  continue  for  about  a  minute. 
Observe  the  change  in  color  from  bright  yellow  to  green.  The  color 
is  best  seen  by  pouring  the  solution  (after  the  action  has  pro- 
ceeded for  about  a  minute)  into  another  test-tube  and  examining 
the  latter  against  a  white  background. 


The  Elements  of  the  Ceria  Earths 

This  group  includes  the  elements,  Ce,  La,  Pr,  Nd  and  Sa. 

CERIUM 

Use  a  solution  of  Ce(N03)a  •  GE^O  of  strength  10  mg.  Ce  per 
cubic  centimeter. 

1.  Action  of  NH-iOH.     (a)  To  2  cc.  of  cerium  nitrate  solution 
add  1  drop  of  dil.  NH^OH  and  then  1  cc.  in  excess.     Note  that  the 
white  precipitate  of  Ce(OH)s  is  insoluble  in  excess  of  the  reagent" 
and  that  it  takes  on  a  violet  tinge  on  exposure  to  air.     Add  an 
excess  (3  cc.)  of  dil.  HC1,  agitate  the  mixture  and  observe  that  the 
precipitate  dissolves.     (6)  In  a  test-tube  treat  2  cc.  of  cerium 
nitrate  solution  with  2  or  3  drops  of  a  strong  aqueous  solution  of 
H2C4H40e.     Add  a  small  piece  of  litmus  paper  and  then  dilute 
NEUOH  to  alkaline  reaction.     Note  the  non-formation  of  a  pre- 
cipitate (distinction  from  Y). 

2.  Action  of  NaOH.     Treat  2  cc.  of  cerium  nitrate  solution 
with  2  drops  of  NaOH  solution  and  add  1  cc.  in  excess.     Note 
that  the  hydroxide  is  insoluble  in  excess. 

3.  Action  of  (NH^S.     To  2  cc.  of  cerium  nirate  solution  add 
1  cc.  of  dil.  NH40H  and  treat  the  mixture  with  H2S.     Note  that 
the  precipitate  remains  unchanged  and  that  it  is  insoluble  in 
excess. 

4.  Action  of  Na2COs.     In  a  test-tube  treat  2  cc.  of  cerium 
nitrate  solution  with  one  drop  of  Na2CO3  solution  and  then  add  1 
cc.  in  excess.     The  white  gelatinous  precipitate  is  cerous  car- 


CERIUM  51 

bonate.  Shake  the  suspended  precipitate  vigorously  and  allow  it 
to  stand  for  about  two  minutes.  Observe  that  the  precipitate 
has  become  crystalline.  Note.  The  same  result  is  obtained 
with  (NH^COs.  The  precipitate  is  however,  soluble  in  a  large 
excess  of  the  reagent.  On  boiling  the  solution,  the  carbonate  repre- 
cipitates. 

5.  Action  of  Oxalic  Acid.     To  2  cc.  of  cerium  nitrate  solution, 
add  1  cc.  of  oxalic  acid  solution.     The  gelatinous  precipitate  is 
cerous  oxalate.     Shake  the  precipitate  vigorously  and  allow  it  to 
stand  for   several  minutes.     Observe   that   the   precipitate  has 
become  crystalline.     Divide  the  precipitate  into  two  equal  por- 
tions.    To  the  first,  add  2  cc.  of  oxalic  acid  and  observe  that  the 
precipitate  does  not  dissolve  (distinction  from  Zr).     To  the  other 
portion  add  5  cc.  dil.  HC1  and  shake  the  mixture  vigorously. 
Observe  that  the  precipitate  is  practically  insoluble. 

6.  Action  of  K2SO4.     In  a  test-tube  treat  2  cc.  of  cerium  solu- 
tion with  2  cc.  of  a  saturated  aqueous  solution  of  K^SO.*.     Heat 
the  solution  to  boiling  and  observe  the  formation  of  a  white 
crystalline  precipitate.     Its  formula  is  062(804)3-8X2804   (dis- 
tinction from  Al,  Be,  and  Y).     Add  to  the  precipitate  2  cc.  dil. 
HC1  and  agitate  the  mixture.     Observe  that  the  precipitate  dis- 
solves. 

7.  Action  of  HF.    In  a  lead  or  platinum  crucible,  treat  2  cc.  of 
cerium  nitrate  solution  with  2  cc.  of  48  per  cent  HF.     The  gelatin- 
ous precipitate  is  CeFs. 

8.  Action  of  NaoS2O3.     To  2  cc.  of  cerium  nitrate  solution  add 
0.2  g.  Na2S2Os.     Shake  the  tube  till  solution  takes  place  and  then 
heat  the  solution  to  boiling.     The  slight  turbidity  which  forms  is 
due  to  the  separation  of  sulphur,  but  no  appreciable  amount  of 
cerium  is  carried  down  (distinction  from  Zr  and  Th) . 

9.  Action  of  H2O2.     (a)  Treat  2  cc.  of  cerium  nitrate  solution 
in  a  test-tube  with  1  cc.  of  3  per  cent  H202.     Observe  that  no  pre- 
cipitate or  coloration  is  formed.     Now  add  1  cc.  of  dil.  NH4OH 
and  observe  the  formtion  of  a  reddish-orange  precipitate  resembling 
Fe(OH)s.     The  reddish  precipitate  is  called  cerium  perhydroxide 
and  possesses  the  formula  CefOH)3-OOH.     The  same  result  is 
obtained  if  the  order  of  the  addition  of  the  reagent  is    reversed; 
i.e.,  if  the  H202  is  added  to  the  white  precipitate  of  Ce(OH)3 
formed  by  adding  1  cc.  of  dil.  NH4OH  to  2  cc.  of  cerium  solution. 
This  reaction  serves  as  a  very  sensitive  test  for  Ce, 


52  RARER  ELEMENTS 

(b)  Sensitiveness  of  the  Test.  In  a  100  cc.  graduated  cylinder, 
dilute  1  cc.  of  cerium  nitrate  solution  with  water  to  100  cc.  Mix 
thoroughly  and  reserve  some  of  this  solution  for  Exp.  106 
below.  To  2  cc.  of  this  solution  (.02  mg.  Ce)  add  1  drop  of  dilute 
NELiOH  and  1  drop  of  3  per  cent  H202.  Note  the  yellow  color  of 
the  solution. 

10.  Action  of  H2O2  in  NH4C2H3O2  Solution,     (a)  To  2  cc. 
of  cerium  nitrate  solution  add  1  cc.  of  NIL^HsC^  solution  and 
1  cc.  of  3  per  cent  H202.     Shake  the  solution  for  several  minutes 
and  allow  it  to  stand.     Observe  that  the  yellow  color  becomes 
brown  and  that  finally  a  reddish  precipitate  forms.     This  is  a  very 
sensitive  test. 

(b)  Sensitiveness  of  the  Test.  To  2  cc.  of  the  dilute  cerium 
solution  reserved  in  Exp.  96  add  1  drop  of  NH4C2HsO2  solution  and 
boil.  Now  add  1  drop  of  3  per  cent  H2O2  and  note  the  yellow 
turbidity  which  results. 

11.  Action  of  Br  and  NaOH.    In  a  test-tube  treat  1  cc.  of 
cerium  solution  with  1  cc.  of  NaOH  solution  and  3  cc.  of  a  saturated 
aqueous  solution  of  bromine.     Shake  the  solution  and  allow  it  to 
stand.    The    yellow    precipitate    which    forms    is    Ce02-3H20 
(method  of  separating  Ce  from  La,  Pr,  and  Nd). 

12.  Oxidation  of  Cerous  to  Ceric  Salts. 

(a)  By  means  of  Ammonium  Persulphate.    To  2  cc.  of  cerium 
nitrate  solution  in  a  test-tube  add  1  cc.  of  dil.  H2S04  and  0.2  g. 
(NH4)2S2Os.    Heat  the  mixture  to  boiling  and  boil  for  a  few  min- 
utes.    Note  the  yellow  coloration  (method  of  detecting  Ce  in  the 
presence  of  La,  Pr,  Nd,  and  Th). 

(b)  By  Means  of  NaBiOs.     To  2  cc.  of  cerium  nitrate  solution 
add  2  cc.  of  dil!  HNOs  and  0.1  g.  NaBiOa.     Warm  the  mixture 
gently  and  allow  it  to  stand.     Note  orange  color  of  the  super- 
natant liquid. 

(c)  By  Means  of  PbO2+HNO3.    Treat  2  cc.  of  cerium  nitrate 
solution  with  1  g.  of  Pb02  and  1  cc.  of  cone.  HNOs.     Boil  the  mix- 
ture  and  allow  it   to   settle.      Observe  the  color  of  the  clear 
solution. 


LANTHANUM  53 


LANTHANUM 

Use  a  solution  of  La(N03)s-6H20  of  strength  10  mg.  La  per 
cubic  centimeter. 

1.  Action  of  NH4OH.     (a)  To  2  cc.  of  lanthanum  nitrate  solu- 
tion add  2  drops  of  dil.  NH4OH.    The  white  precipitate  which 
forms  is  a  basic  salt.     Add  1  cc.  of  dil.  NH4OH  in  excess  and  observe 
that  the  precipitate  is  insoluble  in  excess.     (6)  Treat  in  a  test-tube 
2  cc.  of  lanthanum  solution  with  1  cc.  of  a  strong  aqueous  solution 
of  H2C4H406.     Now  add  dil.  NH4OH  (about  3  cc.)  until  the 
resulting  solution  is  alkaline.     Observe  that  no  precipitate  forms 
(distinction  from  Y). 

2.  Action  of  NaOH.    In  a  test-tube  treat  2  cc.  of  lanthanum 
nitrate  solution  with  1  drop  of  NaOH  solution.     The  white  pre- 
cipitate is  La  (OH)  3.     Add  1  cc.  of  NaOH  in  excess  and  observe 
that   the  precipitate    is   insoluble  in   excess.    Note.     La(OH)3 
is  the  strongest  base  of  the  rare  earths.     It  turns  red  litmus  blue, 
liberates  NHs  from  NH4  salts  and  absorbs  CO2  from  the  air. 
Observe  that  the  precipitate  does  not  change  in  color  on  exposure 
to  the  air  (distinction  from  Ce) . 

3.  Action  of  (NH4)2S.    To  2  cc.  of  La(N03)s  solution  add  1  cc. 
of  dil.  NH4OH  and    treat  the  mixture  with  H2S.     The  white 
precipitate  is  La(OH)3. 

4.  Action  of  (NH4)2COs.     In  a  test-tube  treat  2  cc.  of  lan- 
thanum nitrate  solution  with  1  drop  of  (NH4)2COs  solution  and 
then  add  1  cc.  in  excess.     Note  that  the  precipitate  is  gelatinous 
when  first  formed,  that  it  is  practically  insoluble  in  excess  of  the 
precipitant  and  that  after  standing  the  precipitate  becomes  crys- 
talline. The  formula  for  the  crystalline  salt  is  La2COs  •  (NH4)2CO3  • 
4H20.    Note.    Na2COs  gives  a  precipitate  of  analogous  compo- 
sition. 

5.  Action  of  Oxalic  Acid.     Treat  2  cc.  of  lanthanum  nitrate 
solution  with  1  drop  of  oxalic  acid  solution  and  then  add  1  cc.  in 
excess.     Note  that  the  white  precipitate  of  lanthanum  oxalate 
which  forms  is  insoluble  in  an  excess  of  the  reagent.    Allow  the 
precipitate  to  settle  and  pour  off  the  clear  solution.     To  the  pre- 
cipitate in  the  tube  add  5  cc.  dil.  HC1,  mix  thoroughly  and  heat. 
Observe   that   the   precipitate   dissolves    (difference   from   Th). 
Note.     (NH4)2C204  gives  similar  results. 


54  RARER  ELEMENTS 

6.  Action  of  K2SO4.     To  2  cc.  of  La(N03)3  solution  add  2  cc. 
of  a  saturated  aqueous  solution  of  K^SCU.     Shake  the  tube  vigor- 
ously and  allow  it  to  stand  for  five  minutes.     Observe  the  forma- 
tion of  a  crystalline  precipitate.     The  formula  for  the  precipitate 
is  La2 (804)3-3X2804.    Note.    La2 (804) 3  is  more  soluble  in  cold 
than  in  hot  water.     100  parts  of  water  at  0°  dissolve  3  g.  of  the 
salt  while  at  100°  only  0.3  g.  are  dissolved. 

7.  Action  of  HF.     In  a  lead  or  platinum  crucible,  treat  2  cc.  of 
lanthanum  nitrate  solution  with  1  cc.  of  48  per  cent  HF.     The 
white  gelatinous  precipitate  is  LaFs  •  3H20. 

8.  Action  of  Na2S2Os.    To  2  cc.  of  lanthanum  nitrate  solution 
add  0.2  g.  Na2S203.     Shake  the  tube  till  the  salt  dissolves.     Heat 
the  solution  to  boiling.     The  cloud  which  forms  is  due  to  the 
separation  of  sulphur  resulting  from  the  decomposition  of  some 
of  the  thiosulphate;  but  no  La  precipitates. 


Praseodymium  and  Neodymium 

In  1885  Auer  von  Welsbach  showed  that  the  element  didymium 
was  composed  of  the  two  elements  praseodymium  and  neodymium. 
The  salts  of  the  former  are  green  while  those  of  the  latter  are  pink 
or  violet.  They  may  be  identified  by  the  characteristic  absorp- 
tion spectra  which  are  given  by  the  solutions  of  their  soluble  salts. 
Pr  gives  bands  in  the  blue  and  violet,  while  Nd  shows  bands  in  the 
yellow  and  green.  In  their  chemical  properties,  the  salts  of  these 
metals  resemble  each  other  so  closely,  that  up  to  the  present  time 
it  has  not  been  possible  by  ordinary  analytical  reactions  to  sep- 
arate them.  Von  Welsbach  effected  their  separation  by  a 
long  series  of  fractional  crystallizations  of  their  double  alkali 
nitrates. 

PRASEODYMIUM 

Use  a  solution  of  Pr(NO3)3-6H2O  of  strength  10  mg.  Pr  per 
cubic  centimeter. 

1.  Action  of  NH4OH  and  (NH4)2S.  (a)  To  2  cc.  of  Pr  solu- 
tion add  1  drop  of  dil.  NH40H  and  then  1  cc.  in  excess.  The 
slimy  green  precipitate  is  Pr(OH)3.  Note.  NaOH  gives  the  same 
product. 


NEODYMIUM  55 

(6)  Pass  H2S  into  the  suspended  precipitate  and  observe  that 
there  is  no  visible  change.  Note.  The  sulphide  does  not  form  in 
the  wet  way. 

2.  Action  of  Na2CO3.     Treat  in  a  test-tube  2  cc.  of  Pr(N03)3 
solution  with  2  drops  of  Na2C03  solution.     Note  the  formation  of  a 
green  precipitate.     Now  add  1  cc.  of  Na2CO3  in  excess,  shake  and 
allow  the  tube  to  stand.     Observe  that  the  precipitate  becomes 
crystalline.     Its  formula  is  K2CO3  •  Pr2(C03)3  •  12H2O. 

3.  Action  of  Oxalic  Acid.     To  2  cc.  of  Pr(NO3)3  solution,  add 
1  drop  of  oxalic  acid  solution  and  then  add  1  cc.  in  excess.     The 
light  green  precipitate  which  forms  is  Pr2(C204)3-10H20.     Pour 
off  the  clear  solution,  add  5  cc.  of  dil.  HC1  and  heat  the  mixture 
to  boiling.     Observe  that  the  precipitate  does  not  readily  dissolve. 

4.  Action  of  K2SO4.     In  a  test-tube  treat  2  cc.  of  Pr(NO3)3 
solution  with  2  cc.  of  a  saturated  aqueous  solution  of  K2SO4. 
Shake  the  tube  vigorously  for  one  minute  and  allow  it  to  stand 
for  fifteen  minutes.     The  crystalline  precipitate  which  separates 
is3K2S04-Pr2(S04)3-H20. 

5.  Action  of  HF.     In  a  lead  or  platinum  crucible,  treat  2  cc. 
of  Pr(N03)3  with  2  cc.  of  48  per  cent  HF.     The  gelatinous  precip- 
itate is  PrF3. 

6.  Action  of  Na2S2O3.     To  2  cc.  of  Pr(NO3)3  in  a  test-tube,  add 
0.2  g.  Na2S203.     Shake  the  tube  till  solution  takes  place.     Now 
heat  the  solution  to  boiling.     The  slight  cloud  which  forms  is  due 
to  the  separation  of  sulphur  resulting  from  the  decomposition  of 
some  of  the  thiosulphate;  but  no  Pr  precipitates. 

NEODYMIUM 

Use  a  solution  of  Nd(NO3)3  •  6H20  of  strength  10  mg.  Nd  per 
cubic  centimeter. 

1.  Action  of  NH4OH  and  (NH4)2S.     (a)  To  2  cc.  of  Nd(N03)3 
solution  add  1  drop  of  dil.  NH4OH  and  then  1  cc.  in  excess. 
Observe  that  the  bluish- white  precipitate  of  Nd(OH)3  is  insoluble 
in  an  excess  of  the  reagent. 

(6)  Pass  H2S  through  the  suspended  precipitate  and  note  that 
the  precipitate  remains  unchanged  in  appearance.  Note.  Nd2S3 
does  not  form  in  the  wet  way. 

2.  Action  of  Na2CO3.     In  a  test-tube  treat  2  cc.  of  Nd(N03)3 
solution  with  2  drops  of  Na2C03  solution.     Note  the  formation  of  a 


56  RARER  ELEMENTS 

purplish-white  gelatinous  precipitate.     Now  add  1  cc.  of 

in  excess;  shake  the  mixture  and  observe  that  the  precipitate  does 

not  become  crystalline. 

3.  Action  of  Oxalic  Acid.     To  2  cc.  of  Nd(NOs)3  solution  in  a 
test-tube  add  1  drop  of  oxalic  acid  and  then  1  cc.  in  excess.     The 
rose-colored    precipitate   is   neodymium   oxalate   possessing   the 
formula  Nd2(C204)3-10H20.    Allow  the  precipitate  to  settle  and 
pour  off  the  clear  solution.     To  the  precipitate  in  the  tube  add 
5  cc.  dil.  HC1  and  heat  the  mixture  to  boiling.     Observe  that  the 
precipitate  does  not  readily  dissolve. 

4.  Action  of  K2SO4.    In  a  test-tube  treat  2  cc.  of  Nd(N03)3 
solution  with  2  cc.  of  a  saturated  aqueous  solution  of  K2S04. 
Shake  the  tube  vigorously  for  about  one-half  minute  and  allow 
it  to  stand  for  about  fifteen  minutes.     Note  the  crystalline  pre- 
cipitate which  forms. 

5.  Action  of  HF.     In  a  lead  or  platinum  crucible,  treat  2    cc. 
of  Nd(NO3)3  solution  with  2  cc.  of  48  per  cent  HF.     The  gela- 
tinous precipitate  is  NdFs. 

6.  Action  of  Na2S2O3.    To  2  cc.  of  Nd(N03)a  solution  in  a 
test-tube,  add  0.2  g.  NaoS20s.     Shake  the  mixture  till  solution 
takes  place,  and  then  heat  the  solution  to  boiling.     The  cloudy 
solution  which  results  is  due  to  the  separation  of  sulphur  resulting 
from  the  decomposition  of  some  of  the  thiosulphate;   but  no  Nd 
precipitates. 

The  Elements  of  the  Yttria  Earths 

The  elements  belonging  in  this  group,  arranged  in  the  order  of 
increasing  atomic  weight,  are  Sc,  Y,  Eu,  Tb,  Gd,  Dy,  Ho,  Er,  Tu, 
Yb,  and  Lu.  The  most  important  of  this  group  of  elements  are 
Y  and  Er. 

YTTRIUM 

Use  a  solution  of  Y(NO3)3-6H20  of  strength  10  mg.  Y  per 
cubic  centimeter. 

1.  Action  of  NH4OH,  (NH4)2S  and  NaOH.  (a)  To  2  cc.  of 
Y(NOs)3  solution  add  1  drop  of  dil.  NH4OH  and  then  1  cc.  in 
excess.  The  white  gelatinous  precipitate  is  Y(OH)s.  (6)  Pass 
into  the  mixture  and  observe  that  the  precipitate  remains 


YTTRIUM  57 

unchanged,  (c)  To  2  cc.  of  Y(N03)3  solution  add  1  drop  of  NaOH 
solution  and  then  1  cc.  in  excess.  Note  that  the  precipitate  of 
Y(OH)s  is  insoluble  in  excess. 

2.  Action  of  Na2CO3.     In  a  test-tube,  treat  2  cc.  of  Y(N03)3 
solution  with  1  drop  of  Na2C03  solution.     The  precipitate  is 
Y2(COs)3-3H20.    Add  3  cc.  of  Na2C03  solution  in  excess  and 
shake  the  mixture.     Observe  that  the  precipitate  dissolves  in  an 
excess  of  the  reagent.    The  solution  contains  a  double  carbonate  of 
the  formula  Na2CO3  •  Y2(C03)3  -  4H2O. 

3.  Action  of  (NH4)2CO3.    To  2  cc.  of  Y(N03)3  solution  add  1 
drop  of  (NH4)2C03  solution.     Note  the  precipitation  of  Y2(C03)3. 
Now  add  an  excess  (3  cc.)  of  (NH^COs  and  agitate  the  mixture. 
Observe  that  the  precipitate  dissolves  owing  to  the  formation  of  a 
double  carbonate  of  NH4  and  Y. 

4.  Action  of  Oxalic  Acid.    In  a  test-tube  treat  2  cc.  of  Y(N03)s 
solution  with  1  drop  of  oxalic  acid  solution.     The  white  precip- 
itate which  forms  is  Y2(C2O4)3-9H2O.    To  the  precipitate  in  the 
tube  add  1  cc.  of  oxalic  acid  solution  in  excess  and  note  that  the 
precipitate  is  insoluble  in  excess.     Pour  off  the  clear  solution,  add 
5  cc.  of  dil.  HC1  to  the  precipitate  and  shake  the  mixture.     Observe 
that  the  precipitate  is  practically  insoluble  in  dil.  HC1.    Note. 
Ytrrium  oxalate  is  difficultly  soluble  in  dil.  HC1.     It  is  somewhat 
soluble  in  a  boiling  solution  of  (NH4)2C2O4,  from  which  on  cooling 
and  diluting  the  oxalate  is  completely  reprecipitated  (distinction 
fromTh). 

5.  Action  of  K2SO4.    To  2  cc.  of  Y(N03)a  solution  contained 
in  a  test-tube,  add  2  cc.  of  a  saturated  aqueous  solution  of  K2S04. 
Shake  the  tube  for  a  minute  and  then  allow  it  to  stand  for  ten 
minutes.     Observe  that  no  precipitate  forms  (distinction  from  Th, 
Zr  and  the  ceria  earths). 

6.  Action  of  Na2S2O3.    Treat  2  cc.  of  Y(N03)s  in  a  test-tube 
with  a  few  crystals  of  Na2S2Os.     Shake  the  tube  till  solution  takes 
place.     Note  that  no  precipitate  forms  (distinction  from  Th  and 
Ti) .     On  heating  a  separation  of  S  takes  place  (distinction  from  Zr.) 

7.  Action  of  HF.     In  a  lead  or  platinum  crucible  treat  2  cc.  of 
Y(NOs)3  solution  with  1  cc.  of  48  per  cent  HF.     The  gelatinous 
precipitate  is  YF3  (distinction  from  Al,  Be,  Zr,  and  Ti). 


58  RARER  ELEMENTS 


ERBIUM 

Use  a  solution  of  Er(NO3)3-6H20  of  strength  10  mg.  Er  per 
cubic  centimeter. 

1.  Action  of  NH4OH,  (NH4)2S  and  NaOH,     (a)  To  2  cc.  of 
Er(NOs)3  solution  add  1  drop  of  dil.  NH4OH  and  then  1  cc.  in 
excess.     The  gelatinous  precipitate  which  forms  is  a  basic  salt. 
(6)  Pass  H2S  into  the  suspended  precipitate  and  observe  that  there 
is  no  change  in  the  appearance  of  the  precipitate,     (c)  To  2  cc. 
of  Er(NOs)3  solution  add  1  drop  of  NaOH  and  then  1  cc.  in  excess. 
Note  that  the  precipitate  is  insoluble  in  excess. 

2.  Action  of  Na2CO3  and  (NHi)2CO3.     Treat  2  cc.  of  Er(N03)3 
solution  in  a  test-tube  with  1  drop  of  Na2C03  solution  and  then 
add  3  cc.  in  excess.     Note  the  solubility  of  the  precipitate  in  an 
excess  of  the  precipitant.     (6)  To  2  cc.  of  Er(NOs)3  solution  in  a 
test-tube  add  1  drop  of  (NH4)2C03  solution  and  then  add  4  cc.  in 
excess.     Note  that  the  precipitate  dissolves  in  excess. 

3.  Action  of  Oxalic  Acid.     In  a  test-tube  treat  2  cc.  of  Er(NOs)3 
solution  with  1  drop  of  oxalic  acid  solution  and  then  add  1  cc.  in 
excess.     Note  that  the  precipitate  possesses  a  light  rose  color. 
Pour  off  the  clear  solution.     To  the  precipitate  in  the  tube  add 
5  cc.  of  dil.  HC1  and  shake  the  mixture.     Note  that  the  precipitate 
is  not  readily  soluble  in  dil.  HC1. 

4.  Action  of  K2SO4.     Treat  in  a  test-tube  2  cc.  of  Er(N03)3 
solution  with  2  cc.  of  a  saturated  aqueous  solution  of  K2S04. 
Shake  the  solution  vigorously  for  a  minute  and  allow  it  to  stand 
for  five  minutes.     The  precipitate  is  a  double  sulphate  of  K  and 
Er.     Note.     Heating  promotes  precipitation.     A  solution  of  Y 
of    the  same  concentration    remains  clear  when    treated  with 
K2S04  and  the  solution  heated. 

5.  Action  of  Na2S2O3.     To  2  cc.  of  Er(N03)3  solution  add  0.2 
g.  Na2S2Os  and  shake  the  tube  until  solution  takes  place.     Heat 
the  solution  to  boiling.     Note.     The  cloud  which  forms  is  due  to 
the  separation  of  sulphur  which  results  from  the  decomposition  of 
some  of  the  thiosulphate;  but  no  Er  precipitates. 


VANADIUM  59 


GROUP  3B 


VANADIUM 

Use  a  solution  of  NaV03  of  strength  5  mg.  V  per  cubic  centi- 
meter. 

1.  Action  of  NH4C1.     In  a  test-tube  treat  2  cc.  of  NaV03  solu- 
tion with  0.5  g.  NHiCl.     Shake  the  mixture  vigorously  and  allow 
it  to  stand  for  several  minutes.     The  white  crystalline  precipitate 
which  forms  is  ammonium  metavanadate  NH4V03. 

NaV03+NH4Cl  =  NH4VO3+NaCl. 

Pour  off  carefully  about  1  cc.  of  the  clear  solution.  To  the  precip- 
itate remaining  in  the  test-tube,  add  1  cc.  of  cone.  HNO3.  Observe 
that  the  precipitate  dissolves  completely  yielding  a  yellow  solution. 
Transfer  the  solution  to  a  small  evaporating  dish,  evaporate 
(under  hood)  to  dryness  and  ignite  the  residue.  The  latter  is 
V2Os.  Observe  that  it  is  fusible  but  not  volatile.  Note.  When 
perfectly  pure  ¥205  is  orange-red  in  color. 

2.  Action    of  NH4OH.      (a)    To   1  cc.    of   NaV03   solution 
add  1  cc.  of  dil.  NH4OH.     Observe  that  no  change  takes  place. 
(6)  Dilute  with    water    1  cc.  of  NaVO3  solution  to   10  cc.,  mix 
thoroughly  and  divide  the  solution  into  2  equal  portions.     To 
one  portion  add  1  drop  of  dil.  HC1  and  to  the   other   1   drop 
of  dil.  HN03.     Observe  that   in  each  case  the   solution  becomes 
yellow.     Now  add  a  few  drops  of  dil.  NH4OH  to  each,  making 
each  alkaline.     Note  that  the  color  deepens  in  each  case. 

3.  Action  of  H2S.     In  a  small  beaker  treat  5  cc.  of  NaVOs 
solution  with  2.5  cc.  dil.  HC1.     Dilute  the  solution  with  water 
to  25  cc.  and  treat  it  with  H2S  for  about  a  minute.     Note  the  sep- 
aration of  sulphur.     Filter  and  catch  the  filtrate  in  a  test-tube. 
Observe  that  the  filtrate  is  blue,  due  to  the  reduction  of  the  vana- 
date  to  a  divanadyl  salt. 

2H3VO4+H2S+4HC1  =  V202C14+6H20+S 

4.  Action  of  (NH4)2S.     (a)  In  a  test-tube  treat  2  cc.  of  NaVO3 
solution  with  2  cc.  of  dil.  NH4OH  and  then  bubble  H2S  through  the 


60  RARER  ELEMENTS 

solution.  Note  the  changes  in  color  from  reddish-yellow  to 
violet-red.  Note.  It  is  probable  that  a  thio  salt,  ((NH^sVS^ 
forms. 

(6)  Formation  and  Properties  of  7285.  Acidify  the  above 
solution  by  slowly  adding  to  it  5  cc.  of  dil.  HC1.  When  effer- 
vescence ceases,  filter  off  the  ¥285  and  wash  it  twice  with  5  cc. 
portions  of  water.  Puncture  the  filter  and  wash  the  precipitate 
into  a  test-tube  with  about  5  cc.  of  water.  Allow  the  precipitate 
to  settle  and  carefully  decant  the  water.  Divide  the  suspension  of 
¥285  into  three  equal  portions.  To  the  first  in  a  test-tube  add  2  cc. 
of  dil.  HNOs  and  boil  the  mixture  for  a  minute.  Observe  that  the 
precipitate  dissolves  with  the  separation  of  sulphur.  Treat  the 
second  portion  with  2  cc.  of  dil.  NH^OH  and  heat  the  mixture  to 
boiling.  Note  that  the  precipitate  dissolves  with  the  formation  of 
a  yellow  solution.  To  the  third  portion  in  a  test-tube  add  2  cc. 
of  NaOH  solution.  Note  how  readily  solution  takes  place. 

5.  Action  of  Reducing  Agents. 

(a)  Tartaric  Acid.  To  2  cc.  of  NaVOs  solution  add  a  few  drops 
of  a  saturated  aqueous  solution  of  H^C-tH^Oe.  Observe  the  red- 
dish-yellow color  of  the  solution.  Now  boil  the  solution  for  a  few 
moments  and  observe  the  further  change  in  color  from  green  to 
blue.  Note.  The  blue  color  is  due  to  the  formation  of  a  divanadyl 
salt  (V202)tJ. 

(6)  SnCl2.  Treat  2  cc.  of  NaVOs  solution  in  a  test-tube  with 
1  cc.  of  SnCl2  solution  and  heat  the  tube  to  boiling.  Note  the  blue 
color. 

(c)  Oxalic  Acid.    To  2  cc.  of  NaVOs  solution  add  1  cc.  of 
oxalic  acid  solution  and  heat  the  tube  to  boiling.     Note  the 
changes  in  color  from  yellow  to  blue. 

(d)  H2SO3.    In  a  test-tube  treat  2  cc.  of  NaVOs  solution  with 
1  cc.  of  dil.  HC1  and  0.2  g.  anhydrous  Na2S03.    Boil  the  solution 
and  note  the  blue  color  which  develops. 

(e)  Zn+HCl.    To  2  cc.  of  NaV03  solution  in  a  test-tube  add 
1  cc.  of  dil.  HC1  and  a  small  piece  of  zinc.    Heat  the  tube  to  boiling 
and  note  reduction 

6.  Action  of  H2O2.     (a)  Treat  2  cc.  of  NaV03  solution  with 
1  cc.  of  dil.  HC1  and  2  drops  of  3  per  cent  H202.     Note  that  the 
solution  becomes  red  due  to  the  formation  of  pervanadic  acid 
(HV04). 

(6)  Delicacy  of  the  Test.   Dilute  1  cc.  of  NaV03  solution  with 


LITHIUM  61 

water  to  25  cc.  To  2  cc.  of  the  well-mixed  solution  add  1  drop  of 
dil.  HC1  and  1  drop  of  3  per  cent  H^Cb.  Note  that  the  solution 
acquires  a  light  yellow  color. 

7.  The  Oxidation  of  a  Vanadyl  Salt  to  a  Vanadate  by  Means 
of  Na2O2  in  NaOH  Solution.  In  a  test-tube  treat  2  cc.  of  NaVOs 
solution  with  2  cc.  of  dil.  NEUOH.  Pass  EbS  into  the  solution 
until  it  becomes  violet.  Transfer  the  solution  to  a  small  beaker 
and  add  5  cc.  of  dil.  HNOs.  Note  the  separation  of  ¥285.  Boil 
the  mixture  for  one  or  two  minutes  and  observe  that  the  ¥285 
dissolves,  forming  a  blue  solution.  (This  blue  solution  contains  a 
divanadyl  salt) .  Filter  off  the  sulphur  which  separates  and  catch 
the  filtrate  in  an  evaporating  dish.  Render  the  solution  alkaline 
with  NaOH,  add  0.2  g.  Na202  and  boil  down  to  about  0.5  cc. 
Acidify  the  solution  with  dil.  HNOs,  stirring  the  mixture  thor- 
oughly before  testing  with  litmus  and  finally  add  a  few  drops 
of  3  per  cent  H202.  A  reddish-brown  color  shows  the  presence 
of  a  vanadate. 


GROUP  V.    LITHIUM,  RUBIDIUM  AND  CAESIUM 

LITHIUM 

Use  a  solution  of  LiCl  of  strength  10  mg.  Li  per  cubic  centi- 
meter. 

1.  Action  of  H2PtCl6.    Evaporate  2  cc.  of  LiCl  solution  to  0.5 
cc.    Cool.    Add  three  drops  of  a  10  per  cent  H^PtCle  solution  and 
stir  the  mixture  with  a  glass  rod.     Note  that  no  precipitate  forms 
(distinction  from  K,  NH4,  Rb  and  Cs). 

2.  Action  of  Na3Co(NO2)e.    To  2  cc.  of  LiCl  solution  add  an 
equal  volume  of  NasCo  (N02)  G  solution.     Shake  the  mixed  solution. 
Note  the  absence  of  a  precipitate  (distinction  from  K,  NELi,  Cs  and 
Rb). 

3.  Action  of  Na2HPO4.     In  a  test-tube  treat  2  cc.  of  LiCl 
solution  with  1  cc.  of  Na2HP04  solution.     Heat  the  tube  to  boiling 
and  note  the  formation  of  a  crystalline  precipitate. 

3LiCl+Na2HP04  =  Li3P04+2NaCl+HCl. 

Note.    For  complete  precipitation,  NaOH  solution  should  be 
added  with  the  Na2HP04  until  the  resulting  mixture  is  just  alkaline. 


62  RARER  ELEMENTS 

The  mixture  should  then  be  evaporated  to  dryness  and  the  residue 
treated  with  a  little  water  to  which  some  NH^OH  has  been  added. 
Under  these  conditions  very  small  amounts  of  Li  will  yield  a  precip- 
itate of  2Li3P04  -H20. 

4.  Action  of  KF.     To  2  cc.  of  LiCl  solution  add  1  cc.  KF  solu- 
tion.    The  precipitate  is  LiF  (distinction  and  method  of  separation 
from  K,  Rb  and  Cs  and  from  Na  when  the  latter  is  not  present 
in  too  large  amount). 

5.  Action  of   (NH4)2CO3.     (a)  In  a  test-tube  treat   2  cc.  of 
LiCl  solution  with  2  drops  of  diL  NHiOH  and  1  cc.  of  (NH4)2C03 
solution.     Note  that  no  precipitate  forms,     (b)  Evaporate  10  cc. 
of  LiCl  solution  to  2  cc.     Cool  the  solution  thoroughly  and  transfer 
it  to  a  test-tube.     Add  2  drops  of  dil.  NH4OH  and  1  cc.  of 
(NH4)2COs  solution.     Heat  and  shake  the  tube.     The  crystalline 
precipitate  which  forms  is  Li2C03.     Allow  the  precipitate  to  settle 
and  decant  the  clear  solution.     Dissolve  the  precipitate  in  a  little 
dil.  HC1  and  reserve  this  solution  for  the  flame  and  spectroscopic 
tests. 

Note.  LiC03  is  about  one-half  as  soluble  at  100°  as  it  is  at  10°; 
hence  heating  favors  precipitation.  LiC03  is  prevented  from  pre- 
cipitating by  the  presence  of  a  considerable  quantity  of  alkali  or 
NH4  salts.  Hence  this  reaction  is  not  suitable  for  the  detection 
of  Li. 

6.  Flame  and  Spectroscopic  Tests.     Dip  a  platinum  wire  into 
the  solution  of  LiCl  formed  at  the  end  of  Exp.  5  and  hold  it  in  the 
flame.     Dip  again  and  hold  in  the  flame  and  repeat  this  operation 
until  sufficient  salt  fuses  on  the  wire  to  give  a  crimson  color  to  the 
flame  which  lasts  for  a  number  of  seconds.     Examine  the  flame 
with  a  spectroscope  and  record  your  observations.     Note.     In  the 
presence  of  much  Na,  the  color  is  obscured,  but  maybe  seen 
through  a  cobalt  glass.     Anhydrous  LiCl  is  soluble  in  a  mixture  of 
ether  and  alcohol  (method  of  separation  from  the  remaining  metals 
of  this  group). 

RUBIDIUM 

Use  a  solution  of  RbCl  of  strength  10  mg.  Rb  per  cubic  centi- 
meter. 

1.  Action  of  H2PtCl6.  Evaporate  2  cc.  of  RbCl  solution  to  0.5 
cc.  Cool.  Add  3  drops  of  10  per  cent  HgPtClen  The  precipitate 

is 


CAESIUM  63 

2.  Action  of  Na3Co(NO2)6.     To  2  cc.  of  RbCl  solution  add  2  cc. 
of  Na3Co(N02)6  solution.     Shake  and  observe  the  formation  of  a 
yellow  precipitate. 

3.  Action  of  SbCla.    In  a  test-tube  treat  2  cc.  of  RbCl  solution 
with  3  cc.  of  SbCls  solution  (containing  100  mg.  Sb  as  SbCls 
in  1  cc.  of  HC1  1:1).     Shake  the  mixed  solution  and  observe  that 
no  precipitate  forms. 

4.  Action  of  H2SnCl6.     Treat  1  cc.  of  RbCl  solution  in  a  test- 
tube  with  1  cc.  of  cone.  HC1  and  2  cc.  of  SnCU  solution  (containing 
100  mg.  Sn  as  SnCU  per  cubic  centimeter).     Shake  the  mixed 
solution  and  observe  that  no  precipitate  forms  (distinction  from  Cs). 

5.  Flame  Coloration.     Evaporate  5  cc.  of  RbCl  solution  to  a 
few  drops.     Dip  platinum  wire  into  the  solution  and  hold  it  in  the 
flame.     Observe  the  violet  color  imparted  to  the  flame. 

6.  Spectroscopic  Test.     Examine  the  Rb  flame  with  a  spec- 
troscope.    Note  the  violet  bands  which  are  more  intense  than  the 
line  given  by  K. 


CAESIUM 

Use  a  solution  of  CsNOs  of  strength  10  mg.  Cs  per  cubic 
centimeter. 

1.  Action  of  H2PtCl6.     Evaporate  2  cc.  of  CsNOs  solution  to 
0.5  cc.     By  means  of  a  dropper,  add  3  drops  of  10  per  cent  H^PtCle 
solution.     The  precipitate  is  Cs2PtCl6. 

2.  Action  of  Na^CofNO^o.     To  2  cc.  of  CsN03  solution  in  a 
test-tube  add  2  cc.  of  NaaCofNC^e  solution.     Shake  the  tube  and 
observe  the  formation  of  a  yellow  precipitate. 

3.  Action  of  SbCla.     In  a  test-tube  treat  2  cc.  CsNOs  solution 
with  3  cc.  of  SbCls  solution  (containing  100  mg.  Sb  as  SbCls  in  1  cc. 
of  HC1  1:1).     Shake  the  tube  vigorously  Jor  one-half  minute  and 
note  the  formation  of  a  crystalline  precipitate  (distinction  and 
method  of  separation  of  Cs  from  all  the  alkali  metals  including 
NH4). 

4.  Action  of  H2SnClG.     To  1  cc.  CsN03  solution  add  1  cc. 
of  cone.  HC1  and  2  cc.  of  SnCU  solution  (containing  100  mg.  Sn 
as   SnCU   per   cubic   centimeter).     Shake   the   tube  vigorously. 
The  white  crystalline  precipitate  which  forms  is  Cs2SnCle.  (dis- 
tinction from  K  and  Rb).     Note.     NHi  salts  give  a  similar  pre- 


64  RARER  ELEMENTS 

cipitate  with  this  reagent,  hence  they  must  be  removed  before  using 
this  reagent  to  test  for  Cs. 

5.  Flame  Coloration.     Introduce  into  the  Bunsen  flame  a  few 
drops  of  CsNOs  solution  on  a  platinum  wire  and  observe  the  red- 
dish-violet color  imparted  to  the  flame. 

6.  Spectroscopic  Test.    With  a  spectroscope  examine  the  flame 
given  by  Cs  salts  and  note  the  characteristic  light  blue  lines. 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 


b^W^fcl^     mJmmiT  •• 

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